Chapter 4

Surfaces

One of the most primitive elements in a three-dimensional model of any design is the surface. As you learned in the previous chapter, once survey information is gathered and points are set with elevations, you can proceed to turn some of that information into an intelligent surface. This chapter examines various methods of surface creation and editing. Then it moves into discussing ways to view, analyze, and label surfaces, and explores how they interact with other parts of your project.

In this chapter, you will learn to:

• Create a preliminary surface using freely available data
• Modify and update a TIN surface
• Prepare a slope analysis
• Label surface contours and spot elevations
• Import a point cloud into a drawing and create a surface model

Understanding Surface Basics

A surface in the AutoCAD^® Civil 3D^® program is generated using the principle of geometric triangulation. At the very simplest, a surface consists of points. In planar geometry, two points can be used to define a line and three points can be used to define a plane. Using this principle, the computer generates a triangular plane using a group of three points (Figure 4.1). Each of these triangular planes shares an edge with another, and a continuous surface is made. This methodology is typically referred to as a triangulated irregular network (TIN), as shown in Figure 4.2. On the basis of Delaunay triangulation, this means that for any given (x,y) point, there can be only one unique z value within the surface (since slope is equal to rise over run, when the run is equal to 0 the result is “undefined”). What does this mean to you? It means standard surfaces have two major limitations:

Figure 4.1 Three points defining a plane

Figure 4.2 A triangulated irregular network, or TIN

Beyond these basic limitations, surfaces are flexible and can describe any object's face in astonishing detail. The surfaces can range in size from a few square feet to square miles and generally process quickly.

There are three main categories of surfaces in Civil 3D: standard surfaces, volume surfaces, and corridor surfaces. A standard surface is based on a single set of points, whereas a volume surface builds a surface by measuring vertical distances between two standard surfaces. Each of these two categories of surfaces can also be a grid or TIN surface. The grid version is still a TIN upon calculation of planar faces, but the data points are arranged in a regularly spaced grid of information. The TIN version is made from randomly located points that may or may not follow any pattern to their location. A corridor surface is generated from a corridor and will be discussed further in Chapter 10.

Creating Surfaces

Before you can analyze a surface, you have to make one. To the land development company today, this can mean pulling information from a large number of sources, including Internet sources, old drawings, and fieldwork. Working with each requires some level of knowledge about the reliability of the information and how to handle it in the Civil 3D software. In this section, we'll look at how you can obtain data from a couple of free sources and bring it into your drawing, create new surfaces, and make a volume surface.

Before creating surfaces, you need to know a bit about the components that can be used as part of a surface definition:

Working with all these elements, you can model and render almost any surface you'd find in the world. In the next section, you'll start building some surfaces.

The Yellow Exclamation Point Flag

At some point you are bound to see a yellow exclamation point status icon in Prospector. This is a flag showing you that some elements are out of date and require rebuilding. In the image shown here, the EG surface needs to be rebuilt because the Point Files branch is out of date.

No matter what type of definition in a surface is out of date, to rebuild the surface right-click on the surface's name (in this example that would be EG) and select Rebuild. You could also select Rebuild Automatic, which would result in the surface always rebuilding when required instead of you always having to manually select Rebuild.

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Free Surface Information

You can find almost anything on the Internet, including information about your project site. Some of this information may be valuable in generating a surface to use for conceptual design. For most users, free surface information can be gathered from government entities as discussed in the following section.

Surfaces from Government Digital Elevation Models

One of the most common forms of free data is the Digital Elevation Model (DEM). These files have been used by the U.S. Department of the Interior's United States Geological Survey (USGS) for years and are commonly produced by government organizations for their GIS systems. The DEM format can be read directly by Civil 3D, but the USGS typically distributes the data in a complex format called Spatial Data Transfer Standard (SDTS). The files can be converted using a freely available program named sdts2dem. This DOS-based program converts the files from the SDTS format to the DEM format you need. Once you are in possession of a DEM file, creating a surface from it is relatively simple, as you'll see in this exercise:

1. Start a new drawing from the _AutoCAD Civil 3D (Imperial) NCS template that ships with Civil 3D. For metric users, use the _AutoCAD Civil 3D (Metric) NCS template.

2. Switch to the Settings tab of Toolspace, right-click the drawing name, and select Edit Drawing Settings.

The Drawing Settings dialog appears.

3. For Imperial users, set the Zone Category to USA, Pennsylvania and set the Coordinate System to NAD83 Pennsylvania State Planes, South Zone, US Foot (PA83-SF), as shown in Figure 4.3, via the Units And Zone tab of the Drawing Settings dialog. For metric users, set the Zone Category to USA, Pennsylvania and set the Coordinate System to NAD83 Pennsylvania State Planes, South Zone, Meter (PA83-S).

Figure 4.3 Imperial coordinate settings for DEM import

4. Accept all other defaults.

5. For all users, once complete, click OK.

The coordinate system of the DEM file that you will import will be set to adjust to the coordinate system of the drawing.

6. From the Home tab ⇒ Create Ground Data panel, choose Surfaces ⇒ Create Surface.

The Create Surface dialog appears. You may notice that there is also an option for Create DEM Surface under the Surfaces drop-down. While this may seem like a prudent option since you are using DEM data, the drawback to that method is that no coordinate transformation is possible — and you need it for this example.

7. Accept the options in the dialog, and click OK to create the surface.

This surface is added as Surface1 to the Surfaces collection.

8. In Prospector, expand the Surfaces ⇒ Surface1 ⇒ Definition branch.

9. Right-click DEM Files and select the Add option (see Figure 4.4).

Figure 4.4 Adding DEM data to a surface

The Add DEM File dialog appears.

10. Use the button to the right of the DEM File Name area to navigate to the Stewartstown_PA.DEM file and click Open.

Remember, all data and drawing files for this book can be downloaded from www.sybex.com/go/masteringcivil3d2013. The DEM file information will populate in the Add DEM File dialog showing that the DEM file you are using is UTM Zone 18, NAD27 datum, meters.

11. In the Add DEM File dialog, click in the Value column next to CS Code to display the ellipsis button; click that button to display the Select Coordinate Zone dialog.

12. Set the Coordinate System Code (CS Code) to match the DEM file by selecting UTM with NAD27 datum, Zone 18, Meter; Central Meridian 75d W (UTM27-18) for both Imperial and metric users, as shown in Figure 4.5, and click OK.

Figure 4.5 Setting the Stewartstown_PA.DEM coordinate zone

This information is necessary to properly translate the DEM's coordinate system to the drawing's coordinate system.

The Add DEM File dialog should now match the one shown in Figure 4.6.

Figure 4.6 Setting the Stewartstown_PA.DEM file properties

13. Click OK in the Add DEM File dialog. Importing this DEM file might take a few minutes. You can check the status of the import in the lower-left corner of the application window. The message will be “Reading points from file” and then “Adding points to surface” with a progress gauge.

14. In Prospector, right-click Surface1 and select Zoom To to bring the surface into view.

15. Right-click the surface in your drawing and select Surface Properties.

The Surface Properties dialog appears. Earlier, in the Create Surface dialog you had allowed the default surface name to be used, which created the name of Surface1. Since the default name does not provide much information, you will now revise the default name to something that offers more information to the user.

16. On the Information tab, change the Name field entry to Stewartstown PA.

17. Change the Surface Style drop-down list to Contours and Triangles, and then click OK to accept the settings in the Surface Properties dialog.

Once you have the DEM data imported, you can pause over any portion of the surface and see that feedback showing the surface elevation is provided through a tooltip. This surface can be used for preliminary planning purposes but isn't accurate enough for construction purposes.

The main drawback to DEM data is the sheer bulk of the surface size and point count. The Stewartstown_PA.DEM file you just imported contains 1.4 million points and covers more than 55 square miles. This much data can be overwhelming, and it covers an area much larger than the typical site. If you try zooming in and out on the surface, you will notice that the computer will be slow as it tries to regenerate the surface with each change. To ease the processing and activate the Level Of Detail display, do the following:

After these steps are complete you will notice a new icon appears in the upper-left corner of your model space, showing you that Level Of Detail is activated. To turn off Level Of Detail, follow the same steps.

Turning on the Level Of Detail display does not change the data in the surface but simply changes what is viewable at the different zoom levels. Figure 4.7 shows the same area of the surface zoomed out and zoomed in before (left) turning on Level Of Detail and after (right). You'll look at some data reduction methods later in this chapter.

Figure 4.7 DEM surface: zoomed out without Level Of Detail (upper left), zoomed out with Level Of Detail (upper right), zoomed in without Level Of Detail (lower left), zoomed in with Level Of Detail (lower right)

In addition to making a DEM a part of a TIN surface, you can build a surface directly from the DEM:

The drawback to this approach is that no coordinate transformation is possible. Because one of the real benefits of using georectified data is pulling in information from differing coordinate systems, we're skipping this method to focus on the more flexible method shown in this exercise. When this exercise is complete, you may close the drawing. Due to the large file size, a finished state of this drawing is not available for download on the book's web page.

Surface from GIS Data

You may run into a situation where an outside firm uses GIS, or perhaps your firm is also using GIS data. Civil 3D understands GIS and can work with the data given. In this section, we'll show you how to import GIS data pertaining to surfaces:

1. Start a new drawing by using the _AutoCAD Civil 3D (Imperial) NCS template and set the Coordinate System to NAD83 Georgia State Planes, West Zone, US Foot (GA83-WF). For metric users, use the _AutoCAD Civil 3D (Metric) NCS template and set the Coordinate System to NAD83, Georgia State Planes, West Zone, Meter (GA83-W).

2. From the Home tab ⇒ Create Ground Data panel, choose Surfaces ⇒ Create Surface From GIS Data.

The Create Surface From GIS Data – Object Options page appears.

3. Set Name to GIS Data, change Description to Import from GIS Data, and set the style to Contours 5 ′ and 25 ′ (Background), or Contours 2 m and 10 m (Background) for metric users as shown in Figure 4.8, and click the Next button.

Figure 4.8 The Create Surface From GIS Data – Object Options page

The Create Surface From GIS Data – Connect To Data page appears.

4. You are importing a SHP file, so change Data Source Type to SHP.

5. Click the ellipsis next to SHP Path. Locate the contours2008.shp file (which you'll find at www.sybex.com/go/masteringcivil3d2013).

The path is now populated with the location of the SHP file, as shown in Figure 4.9.

Figure 4.9 The Create Surface From GIS Data – Connect To Data page

6. Click the Login button.

Don't worry; you won't actually need a username or password to log in.

The Create Surface From GIS Data – Schema And Coordinates page now appears (Figure 4.10).

Figure 4.10 The Create Surface From GIS Data – Schema And Coordinates page

You will notice that the name of the file appears as well as the coordinate system in which the SHP was created. For Imperial users, the NAD83 Georgia State Plane, West Zone, US Foot matches what you set the drawing up with. However, for metric users, the coordinate system of the SHP file is different than the drawing coordinate system as shown in Figure 4.10.

7. Verify that the Contours2008 check box is checked under Feature Class and click Next.

8. On the Create Surface From GIS Data – Geospatial Query page, look at the settings for future reference but do not make any changes (Figure 4.11). Click Next.

Figure 4.11 The Create Surface From GIS Data – Geospatial Query page

9. On the Create Surface From GIS Data – Data Mapping page, click the drop-down list next to GIS Field Elevation and select Elevation, as shown in Figure 4.12.

Figure 4.12 The Create Surface From GIS Data – Data Mapping page

Many dialogs throughout the software use tables such as those shown on this page for you to input data. If at any time the column is not wide enough for you to view all of the content, you may modify the column width by clicking between the column headings.

At the bottom of the Create Surface From GIS Data – Data Mapping page you will notice a field for File Name as well as Save and Open icons. That means you can save the current data mapping information that you've set for future use.

10. Click the Finish button.

11. Dismiss the Panorama and zoom extents to see the surface based on the SHP file (Figure 4.13).

Figure 4.13 The finished imported GIS contours

When this exercise is complete, you may close the drawing. A saved finished copy of this drawing is available from the book's web page with the filename SurfaceGIS_FINISHED.dwg or SurfaceGIS_METRIC_FINISHED.dwg.

This is just another avenue for getting drawings from other sources into Civil 3D. This topic will be discussed in depth in Chapter 18, “Advanced Workflows.”

Surface Approximations

In this section, you'll work with elevated polylines. Later in this chapter, you'll work with a large point cloud delivered as a text file. These polylines are quite common, and historically it can be difficult making an acceptable surface from them.

Surfaces from Polyline Information

One common complaint about converting a drawing full of contours at elevation into a working digital surface is that the resulting contours don't accurately reflect the original data. This is because point information is provided along the contour lines but not in between the contour lines, causing the interpolation between the contours to lack accuracy. Civil 3D includes a series of surface algorithms that work very well at matching the resulting surface to the original contour data by providing additional derived data points. You'll look at those surface edits in this series of exercises.

1. Open the SurfaceFromPolylines.dwg file (or the SurfaceFromPolylines_METRIC.dwg file).

Note that the contours in this file are composed of polylines with elevation values.

2. In Prospector, right-click the Surfaces branch and select the Create Surface option.

The Create Surface dialog appears.

3. Leave the Type field set to TIN Surface but change the Name value to EG-Polylines.

4. Change Description to Surface From Polylines.

5. Click in the Value column next to Style to display the ellipsis button; once it's visible click the ellipsis button to display the Select Surface Style dialog.

6. From the drop-down list, select Contours 1′ and 5′ (Background), or Contours 0.2 m and 1 m (Background) for metric users, and click OK to close the Select Surface Style dialog.

7. Click OK to close the Create Surface dialog.

8. In Prospector, expand the Surfaces ⇒ EG-Polylines ⇒ Definition branches.

9. Right-click Contours and select the Add option.

The Add Contour Data dialog appears.

10. Set Description to Polyline; under Weeding Factors, set Distance to 15 (or 5 for metric users) and Angle to 4 degrees; and under Supplementing Factors, set Distance to 100 (or 30 for metric users) and Mid-Ordinate Distance to 1 (or 0.3 for metric users).

11. Verify that none of the check boxes are checked, as shown in Figure 4.14, and click OK.

Figure 4.14 The Add Contour Data dialog

You will return to the Minimize Flat Areas By options in a bit.

12. At the Select contours: prompt, enter ALL to select all the entities in the drawing and press again to end the command.

You can dismiss Panorama if it appears and covers your screen. Save and keep the drawing open for the next portion of the exercise.

The contour data has some tight curves and flat spots where the basic contouring algorithms simply fail. Zoom into any portion of the site, and you can see these areas by looking for the blue and cyan original contours not matching the new Civil 3D–generated contour, as shown in Figure 4.15.

Figure 4.15 Contour surface without minimizing flat areas

You'll fix that now:

13. In Prospector, expand the Definition branch of the EG-Polylines surface if it's not already open from the previous exercise and right-click Edits.

14. Select the Minimize Flat Areas option to open the Minimize Flat Areas dialog.

Note that the dialog has the same options found in that portion of your original Add Contour Data dialog. The benefit to doing it as two steps instead of one is that you can remove the operation from the Surface Build Operation if it is done separately.

15. Click OK to accept the defaults.

Save and keep the drawing open for the next portion of the exercise.

Now the contours displayed more closely match the original contour information, as shown in Figure 4.16. There might be a few instances where gaps exist between old and new contour lines, but in a cursory analysis, none was off by more than 0.4′ in the horizontal direction — not bad when you're dealing with almost a square mile of contour information.

Figure 4.16 Contour surface with minimizing flat areas

You'll see how this was done in this quick exercise:

16. Zoom into an area with a dense contour spacing and select the surface to make the contextual tab associated with the TIN Surface: EG-Polylines appear.

17. From the TIN Surface contextual tab ⇒ Modify panel, choose Surface Properties to display the Surface Properties dialog.

18. On the Information tab, set Surface Style to Contours And Points and click OK to see a drawing similar to Figure 4.17.

Figure 4.17 Surface data points and derived data points

In Figure 4.17, you're seeing the points the TIN is derived from, with some styling applied to help you understand the creation source of the points. Each point shown as a red + symbol is a point picked up from the contour data itself. The magenta points shown with a circle symbol circumscribed over a + symbol are all added data on the basis of the Minimize Flat Areas edits. These points make it possible for the Civil 3D surface to match almost exactly the input contour data.

When this exercise is complete, you may close the drawing. A saved finished copy of this drawing is available from the book's web page with the filename SurfaceFromPolylines_FINISHED.dwg or SurfaceFromPolylines_METRIC_FINISHED.dwg.

Surfaces from Points or Text Files

Besides receiving polylines, it is common for a surveying company to also send a simple text file with points. This isn't an ideal situation because you have no information about breaklines or other surface features, but it is better than nothing or usually more accurate than a surface based on free data. Because you have the same aerial surface described as a series of points, you'll use them to generate a surface in this exercise:

1. Create a folder on your computer called C:Mastering.

2. Place the Concord Commons.txt file (or Concord Commons_METRIC.txt file for metric users) in your newly created folder.

Doing so ensures that future exercises will function properly.

3. Create a new drawing using the _AutoCAD Civil 3D (Imperial) NCS template. For metric users, use the _AutoCAD Civil 3D (Metric) NCS template.

4. For Imperial users, change the Coordinate System to NAD83 Pennsylvania, South Zone, US Foot (PA83-SF). For metric users, change the Coordinate System to NAD83 Pennsylvania, South Zone, Meters (PA83-S).

5. From the Home tab ⇒ Create Ground Data panel, choose Surfaces ⇒ Create Surface.

The Create Surface dialog appears.

6. Change the Name value to EG, and click OK to close the dialog.

7. In Prospector, expand the Surfaces ⇒ EG ⇒ Definition branches.

8. Right-click Point Files and select the Add option.

The Add Point File dialog shown in Figure 4.18 appears.

Figure 4.18 Adding a point file to the surface definition

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Default Advanced Options

Note that some of the default Advanced Options may vary from user to user so your dialog may not have the same options checked as shown in Figure 4.18. We will confirm that the correct options are selected in a later step.

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9. Set the Specify Point File Format to PNEZD (Comma Delimited).

Make sure it is PNEZD, and not PENZD or your results will be off completely.

10. Click the Browse button.

The Select Source File dialog opens.

11. Navigate to the previously created C:Mastering folder, and select the Concord Commons.txt file (or Concord Commons_METRIC.txt file). Click OK.

12. In the Advanced Options area of the dialog, verify that “Do elevation adjustment if possible” is checked and “Do coordinate transformation if possible” is not checked.

13. Click OK to accept the settings in the Add Point File dialog and build the surface.

Panorama will appear, but you can dismiss it.

14. Right-click EG Surface in Prospector and select the Zoom To option to view the new surface created.

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Surface Snapshots

A surface snapshot captures the surface information in the state when the snapshot was created. If there is a snapshot in a surface, a surface's Rebuild (or surface's Rebuild Automatic) will start at the snapshot since the snapshot summarizes all of the previous build operations.

As mentioned before, a drawing will stay referenced to a point file, and if the point file is moved or deleted, the reference in the drawing will be broken. To prevent this from affecting the surface, you can create a snapshot of the surface while the surface is still working as intended. Then if anything happens to the external data, the surface will not have to go look for it if a snapshot exists.

While referencing an external file is a good reason to create a snapshot, it is not the only reason. Snapshots can be used any time you want to capture the current state of a surface.

If you right-click on a surface's name in Prospector, you will see three options related to snapshots:

Create Snapshot

By creating a snapshot, you add a build operation that captures the surface information in the current state. Once a snapshot is created, the icon next to Definition in the Prospector tree will change to a camera icon.

Remove Snapshot

This option will remove the snapshot from the build operation.

Rebuild Snapshot

Rebuilding the snapshot and rebuilding the surface are in fact two different things. If the operations prior to the snapshot become outdated, you will see a yellow status icon next to its node in the Prospector tree prompting for the snapshot to be rebuilt. You can then choose to rebuild the snapshot if you want the changes to affect the surface or leave the snapshot in place as is if you do not want the changes to affect the surface.

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When this exercise is complete, you may save and keep the drawing open to continue on to the next exercise. Or you may use the saved finished copy of this drawing available from the book's web page (SurfaceFromPoints_FINISHED.dwg or SurfaceFromPoints_METRIC_FINISHED.dwg).

In both the polyline and point file examples, you're making surfaces from the best information available. When you're doing preliminary work or large-scale planning, these types of surfaces are great. For more accurate and design-based surfaces, you typically have to get into field-surveyed information. We'll look at that a little later.

Simply adding surface information to a TIN definition isn't enough. To get beyond the basics, you need to look at the edits and other types of information that can be part of a surface.

Refining and Editing Surfaces

Once a basic surface is built, and, in some cases, even before it is built, you can do some cleanup and modification to the TIN construction that make it much more usable and realistic. Some of these edits include limiting the input data, tweaking the triangulation, adding in breakline information, or hiding areas from view. In this section, you'll explore a number of ways of refining surfaces to end up with the best possible model from which to build.

Surface Properties

The most basic steps you can perform in making a better model are right in the Surface Properties dialog. The surface object contains information about the build and edit operations, along with some values used in surface calculations. These values can be used to tweak your surface to a semi-acceptable state before more manual operations are needed.

In this exercise, you'll go through a couple of the basic surface-building controls that are available. You'll use them one at a time in order to measure their effects on the final surface display.

Figure 4.19 Surface Properties Definition Options

Save and keep the drawing open for the next portion of the exercise.

The Build options of the Definition tab allow you to tweak the way the triangulation occurs. The basic options are listed here:

If you close the Surface Properties dialog and look at the surface, you might not notice the blob area shown in Figure 4.20. It appears that there are a series of blown shots, causing the elevation to dip to zero. In this next portion of the exercise, you'll limit the build options to make that blown surface “disappear.”

Figure 4.20 EG surface showing blown points

6. If you previously closed the Surface Properties dialog, open it again and on the Definition tab expand the Build category.

7. Verify that the Exclude Elevations Less Than value is Yes.

8. Set the value to 200 (60 for metric users) and click OK to accept the settings in the dialog.

Elevations less than 200′ (or 60 m for metric users) will be excluded. A warning message will appear. Civil 3D is warning you that your surface definition has changed.

9. Click Rebuild The Surface to rebuild the surface.

10. Zoom extents to view the full surface.

When it's done, it should look similar to Figure 4.21. Save and keep the drawing open for the next portion of the exercise.

Figure 4.21 EG surface after ignoring low elevations

Although this surface is better than the original, there are still large areas being contoured that probably shouldn't be. By changing the style to review the surface, you can see where you still have some issues:

11. Open the Surface Properties dialog again, and switch to the Information tab.

12. Change the Surface Style field to Contours And Triangles.

13. Click Apply. Doing so makes the changes without exiting the dialog.

14. Drag the dialog to the side so you can see the site.

On the outer edges of the site, you can see some long triangles formed in areas where there was no survey taken but the surface decided to connect the triangles anyway (Figure 4.22, left).

Figure 4.22 EG surface before Maximum Triangle (left) and after (right)

15. In the Surface Properties dialog, switch to the Definition tab.

16. Expand the Build category by clicking the + symbol.

17. Set the Use Maximum Triangle Length value to Yes.

18. In the Maximum Triangle Length value field, enter 300 (or for metric, 90).

19. Click OK to apply the settings and close the dialog.

20. Click Rebuild The Surface to update and dismiss the warning message to see the revised surface (Figure 4.22, right).

When this exercise is complete, you may close the drawing. A saved finished copy of this drawing is available from the book's web page with the filename SurfaceProperties _FINISHED.dwg or SurfaceProperties_METRIC_FINISHED.dwg.

The value is a bit high, but it is a good practice to start with a high value and work down to avoid losing any pertinent data. Setting this value to 225′ (or 70 m) will result in a surface that is acceptable because it doesn't lose a lot of important points. Beyond this, you'll need to look at making some edits to the definition itself instead of modifying the build options.

Surface Additions

Beyond the simple changes to the way the surface is built, you can look at editing the pieces that make up the surface. With your drawing so far, you have merely been building from points. Although this is fine for small surfaces, you need to go further with this surface. In this section, you'll add a few breaklines and a border and then perform some manual edits to your site.

You Can't Always Get What You Want

But sometimes you get what you need. Autodesk has included the ability to reorder the build operations on the Surface Properties Definition tab. If you look at the lower left of the Definition tab shown here, you'll find that there are arrows to the left of the list box showing all the data, edits, and changes you've made to the surface.

As Civil 3D builds a surface, it processes this data and information from top to bottom — in this case, adding points, and then the breaklines, and then a boundary, and so on. If a later operation modifies one of these additions or edits, the later operation takes priority. To change the processing order, select an operation, and then use the arrows at the left to push it up or down within the process. One common example of this is to place a boundary as the last operation to ensure accurate triangulation. You'll look at boundaries in the next section.

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Adding Breakline Information

Breaklines can come from any number of sources. They can be approximated on the basis of aerial photos of the site that help define surface features, or they can be directly input from field book files and the Civil 3D survey functionality. Five types of breaklines are available for use:

In most cases, you'll build your surfaces from standard, proximity, and wall breaklines. In this example, you'll add in some breaklines that describe road and surface features:

1. Open the SurfaceBreaklines.dwg file or the SurfaceBreaklines_METRIC.dwg file.

2. Thaw the _Polylines-Road layer.

The roads are the color red.

3. Select the surface, and then pan and zoom to see that the triangulation lines do not appear along all the breaklines.

4. Unselect the surface by pressing Esc.

5. Select and then right-click on one of the red polylines and choose the Similar option.

All the red polylines are now highlighted.

6. In Prospector, expand the Surfaces ⇒ EG ⇒ Definition branches.

7. Right-click Breaklines and select the Add option.

The Add Breaklines dialog appears.

8. Enter a description if you wish and the settings as shown in Figure 4.23.

Figure 4.23 The Add Breaklines dialog

9. Click OK to accept the settings and close the dialog.

You can dismiss Panorama if it appears.

10. Thaw the _Polylines-Surface layer.

The surface polylines are the color green.

11. Repeat steps 5 through 9 but instead of the red polylines select the green lines on the _Polylines-Surface layer. Change the description to Surface Polylines.

As shown in Figure 4.24, by adding the breaklines you force the TIN lines to align with the breaklines, thus cleaning up the contours and making them follow the ridgelines of the road centerline, gutterlines, and shoulders as well as the changes in grade around the small detention area.

Figure 4.24 EG surface with only contours displayed before breaklines added (left) and after (right)

When this exercise is complete, you may close the drawing. A saved finished copy of this drawing is available from the book's web page with the filename SurfaceBreaklines_FINISHED.dwg or SurfaceBreaklines_METRIC_FINISHED.dwg.

The surface changes reflect the breaklines added. On sites with more extreme grade breaks, such as those that might follow a channel or a site grading, breaklines are invaluable in building the correct surface.

Crossing Breaklines

Invariably, you will see Panorama pop up with a message about crossing breaklines. In general, Civil 3D does not like breaklines that cross themselves. The Resolve Crossing Breaklines tool will let you examine those situations:

1. Click on a surface with breaklines.

2. From the TIN Surface contextual tab ⇒ Analyze panel, choose Resolve Crossing Breaklines.

3. At the Please specify the types of breakline you want to find or [surveyDatabase Figure Surface]: prompt, enter S to select the surface option.

The Crossing Breaklines tab on Panorama lists the crossing breaklines. You can decide how you want to resolve them using Use Higher Elevation, Use Lower Elevation, Use Average Elevation, or Use Specified Elevation, as shown here:

4. Click on each breakline and click the Resolve button, which is located underneath the drop-down list shown here; the conflict disappears from the Crossing Breaklines conflict list.

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Adding a Surface Boundary

In the previous exercise, you fixed some breakline issues. However, in the data presented, the bigger issue is still the number of inappropriate triangles that are being drawn along the edge of the site. It is often a good idea to leave these triangles untouched during the initial build of a surface, because they serve as pointers to topographical data (such as monumentation, control, utility information, and so on) that may otherwise go unnoticed. This is a common problem that can be solved by using a surface border. You can sketch in a polyline to approximate a border, but the Extract Objects from Surface utility gives you the ability to use the surface itself as a starting point.

The Extract Objects from Surface utility allows you to re-create any displayed surface element (contours, border, etc.) as an independent AutoCAD entity. It is important to note that only the objects that are currently visible in the surface style are extractable. In this exercise, you'll extract the existing surface boundary as a starting point for creating a more refined boundary that will limit triangulation:

1. Open the SurfaceBoundary.dwg or SurfaceBoundary_METRIC.dwg file.

2. Select the surface.

3. From the TIN Surface contextual tab ⇒ Surface Tools panel, choose Extract Objects to open the Extract Objects From Surface dialog.

4. Leave the Border object selected and deselect the Major Contour and Minor Contour options, as shown in Figure 4.25.

Figure 4.25 Extracting the border from the surface object

5. Click OK to finish the process. Press Esc to deselect the surface.

A 3D polyline has been created from the surface border.

6. Pick the border 3D polyline.

This polyline will form the basis for your final surface boundary. By extracting the border polyline from the existing surface, you save a lot of time playing connect the dots along the points that are valid. Next, you'll refine this polyline and add it back into the surface as a boundary.

7. In Prospector, right-click Point Groups and select the Properties option. The Point Groups dialog appears.

8. Select _All Points from the list of point groups and then move _All Points to the top of the list using the Move The Selected Item To The Top Of The Order arrow on the right side of the dialog.

9. Click OK to display all your points on the screen.

There are a lot of points, so this might take a minute.

10. Working your way around the site, grip-edit the polyline you created in step 6 to exclude some of the area at the northwest of the site where there are no points.

On a large site, you can see that this is a time-consuming process but worth the effort to clean up the site nicely (Figure 4.26). Thankfully, there are other methods you can use to clean up the surface border; we will discuss these methods in later exercises.

Figure 4.26 Using the grips to adjust the border

11. In Prospector, right-click Point Groups and select the Properties option.

The Point Groups dialog appears.

12. Select the No Display point group from the list and then move No Display to the bottom of the list using the Move The Selected Item To The Top Of The Order arrow on the right side of the dialog.

13. Click OK to turn off the display of all your points on the screen.

If completed, your polyline might look something like Figure 4.27. A saved finished copy of this drawing with the complete polyline is available from the book's web page with the filename SurfaceBoundaryPolyline_FINISHED.dwg or SurfaceBoundary_METRIC_FINISHED.dwg for use in the remaining portion of this exercise.

Figure 4.27 Revised surface border polyline

Just as with breaklines, there are multiple types of surface boundaries:

Outer Boundaries

Use this type to define the outer edge of the shown boundary. When the Non-destructive Breakline option is used, the points outside the boundary are still included in the calculations; then additional points are created along the boundary line where it intersects with the triangles it crosses. This boundary trims the surface for display but does not exclude the points outside the boundary. You'll want to have your outer boundary among the last operations in your surface-building process. Therefore, as future edits are made, you may want to move the Add Boundary build operation back to the bottom of the operations list on the Definition tab in the Surface Properties dialog, as discussed earlier in this chapter.

Show Boundaries

Use this type to show the surface inside a hide boundary, essentially creating a reverse donut effect in the surface display.

Hide Boundaries

Use this type to punch a hole in the surface display for tasks like building footprints or a wetlands area that are not to be touched by design. Hidden surface areas are not deleted but merely not displayed; therefore, the surface inside a hide boundary is still used for calculations such as area or cut/fill.

Data Clip Boundaries

Data clip boundaries place limits on data that will be considered part of the surface from that point going forward. This type is different from an outer boundary in that the data clip boundary will keep the data from ever being built into the surface as opposed to limiting it after the build. Using data clip boundaries is handy when you are attempting to build Civil 3D surfaces from large data sources such as Light Detection and Ranging (LiDAR) or DEM files. Because they limit data being placed into the surface definition, you'll want to have data clips among the first operations in your surface.

The addition of every boundary is considered a separate part of the building operations. This means that the order in which the boundaries are applied controls their final appearance. For example, a show boundary selected before a hide boundary will be overridden by that hide operation. To finish the exercise, you'll add the outer boundary twice, once as a non-destructive breakline and once with a standard breakline, and observe the difference.

14. Open the SurfaceBoundaryPolyline_FINISHED.dwg or SurfaceBoundaryPolyline_METRIC_FINISHED.dwg file.

15. In Prospector, expand the Surfaces branch.

16. Right-click EG and select the Surface Properties option.

The Surface Properties dialog appears.

17. On the Information tab, change the Surface Style to 1′ and 5′ TIN Editing (Ex.), or 1 m and 5 m TIN Editing (Ex.) for the metric users, then click OK.

18. In Prospector, expand the Surfaces ⇒ EG ⇒ Definition branches.

19. Right-click Boundaries and select the Add option.

The Add Boundaries dialog opens (Figure 4.28).

Figure 4.28 Add Boundaries dialog

20. Enter a name if you like and verify that there is a check mark next to the Non-destructive Breakline option; then click OK.

21. Pick the polyline border that you previously extracted and edited; then notice the immediate change.

22. Zoom in on the northwest portion of your site, as shown in Figure 4.29.

Figure 4.29 A non-destructive outer boundary in action

Save and keep the drawing open for the next portion of the exercise.

Notice how the edge of the triangulation includes points shown as a square with a + symbol; these are the additional points created along the boundary line where it intersects with the triangles it crosses. The points you attempted to exclude from the surface are still being included in the calculation of elevations for this point; they are just excluded from the display and calculations. This isn't the result you were after, so let's fix it now.

23. In Prospector, expand the Surfaces ⇒ EG ⇒ Definition branches and select Boundaries.

A listing of the boundaries appears in the preview area of Toolspace.

24. In the preview area at the bottom of Prospector, right-click the boundary you just created and select the Delete option.

25. Click OK in the warning dialog that tells you the selected definition items will be permanently removed from the surface.

In Prospector, you will now see the yellow exclamation point status flag next to the EG branch as well as the definition branch. This is because the surface needs to be rebuilt.

26. Right-click the EG branch and select the Rebuild option to rebuild the surface without the boundary definition.

You can dismiss Panorama if it appears.

27. In Prospector, right-click Boundaries and select the Add option again.

The Add Boundaries dialog appears.

28. This time, leave the Non-destructive Breakline option unchecked, and click OK.

29. Pick the border 3D polyline again.

Notice that no triangles intersect your boundary now where it does not connect points, as shown in Figure 4.30.

Figure 4.30 A destructive outer boundary in action

When this exercise is complete, you may close the drawing. A saved finished copy of this drawing is available from the book's web page with the filename SurfaceBoundary_FINISHED.dwg or SurfaceFromBoundary_METRIC_FINISHED.dwg.

As you have seen, the non-destructive boundary we looked at first is the peacekeeper. It always seeks to find a “common ground” (interpolated elevation) between the two existing points on either side of a TIN line that it crosses, whereas the destructive boundary is so powerful that it cuts off all communication between points inside and outside the boundary.

In spite of adding breaklines and a border, you still have some areas that need further correction or changes.

Surface Cropping

Surface cropping is useful when you are working with a small portion of a much larger surface. A cropped area within a surface becomes a separate surface object (a new surface) to be managed and manipulated on a much smaller scale. In this example, you will create a cropped surface and add it to an existing drawing:

1. Open the SurfaceCropping.dwg or SurfaceCropping_METRIC.dwg file.

2. Select the surface to activate the contextual tab and expand the bottom of the Surface Tools pane.

3. From the Surface Tools expanded panel, choose the Create Cropped Surface option.

You may receive a message box stating that “This drawing must be saved before this command can be used.” If so:

a. Save the drawing.

b. Reselect the Create Cropped Surface option.

The Create Cropped Surface dialog is displayed, as shown in Figure 4.31.

Figure 4.31 The Create Cropped Surface dialog

4. Click the text that says <Selection Method> in the Value column next to Select Crop Area to display the ellipsis button; once it's visible, click the ellipsis button.

5. At the Select first corner or [Object Polygon]: prompt, enter O .

6. At the Select objects: prompt, select the red polyline on the _Cropped layer and press .

7. At the Select point in the area to crop: prompt, click inside the polyline you just selected.

The cropped boundary is now highlighted, and the Create Cropped Surface dialog returns.

8. Left-click inside the Value column next to Drawing For New Surface and select Create A New Drawing from the drop-down list.

9. Click the text that says <Create A New Drawing> in the Value column next to Create A New Drawing to display the ellipsis button and then click that button.

The Select Template dialog opens.

10. Select an appropriate template (either _AutoCAD Civil 3D (Imperial) NCS.dwt or _AutoCAD Civil 3D (Metric) NCS.dwt) and click Open.

The Value column for Create A New Drawing is populated with the next open drawing name, such as Drawing1.dwg. At this point the new drawing has only been created and opened but is not yet saved.

11. In the Value column for New Surface Name, enter Cropped Area.

You can also enter a description for the new surface if desired.

12. Set Surface Style to Contours And Triangles.

13. Click OK to complete the Create Cropped Surface command and create a cropped surface in the new drawing.

14. Switch to the drawing just created and zoom extents to see your newly created cropped surface, as shown in Figure 4.32.

Figure 4.32 The completed cropped surface

When this exercise is complete, you may close the drawing. A saved finished copy of this drawing with the cropped surface is available from the book's web page with the filename SurfaceCropping_FINISHED.dwg or SurfaceCropping_METRIC_FINISHED.dwg.

Manual Surface Edits

In your surface, you have a few “finger” surface areas where the surveyors went out along narrow paths from the main area of topographic data. The nature of TIN surfaces is to connect dots, and so these fingers often wind up as webbed areas of surface information that's not accurate or pertinent. A number of manual edits can be performed on a surface, including adding a boundary. These edit options are part of the definition of the surface and include the following:

Manual editing should always be the last step in updating a surface. Fixing the surface is a poor substitution for fixing the underlying data the TIN is built from, but in some cases, it is the quickest and easiest way to make a more accurate surface.

Point and Triangle Editing

In this section, you'll remove triangles manually, and then finish your surface by correcting what appears to be a blown survey shot.

1. Open the SurfaceEdits.dwg file (or the SurfaceEdits_METRIC.dwg file). Confirm that the EG surface style is set to Contours And Triangles.

2. In Prospector, expand the Surfaces ⇒ EG ⇒ Definition branches.

3. Right-click Edits and select the Delete Line option.

Note that if you have Level Of Detail turned on, a red circle warning will appear if you are not zoomed in enough to view the true triangulation.

4. At the Select edges: prompt, enter F to use the Fence selection mode.

In Fence selection mode you will draw a multisegment selection line and any objects that cross the line will be selected. Alternatively you could enter C to use the Crossing selection mode, which uses a selection window and selects all objects that have at least a portion within the window.

5. Use a Center Osnap to pick the circle labeled A at the lower right of the pick area, as shown in Figure 4.33; move to the upper-left corner as shown; use a Center Osnap to pick the circle labeled B; and press twice.

Figure 4.33 Using a Crossing Window selection

6. Right-click or press to finish the selection set.

7. Repeat this process, removing triangles until your site resembles the image on the right in Figure 4.34.

Figure 4.34 Surface before removal of extraneous triangles (left) and after (right)

8. Zoom to the portion of your site with the red circle labeled C, and you'll notice a collection of contours that seems out of place.

9. Change Surface Style to Contours And Points.

10. In Prospector, right-click Edits again and select the Delete Point option.

11. Zoom in on the area very close.

You will find a series of + point markers in the area with close contours. These are blown shots and the contours are simply obeying the point elevation. In this case, it is 0.

12. Select each of the three markers and delete them; then notice the immediate change in the contouring.

When this exercise is complete, you may save and keep the drawing open to continue on to the next exercise or use the saved finished copy of this drawing available from the book's web page (SurfaceEdits_FINISHED.dwg or SurfaceEdits_METRIC_FINISHED.dwg).

Surface Smoothing

One common complaint about computer-generated contours is that they're simply too precise. The level of calculations in setting elevations on the basis of linear interpolation along a triangle leg makes it possible for contour lines to be overly exact, ignoring contour line trends in place of small anomalies of point information. Under the eye of a board drafter, these small anomalies were averaged out, and contours were created with smooth flowing lines.

While you can apply object-level smoothing as part of the contouring process, this process smooths the end result but not the underlying data. In this section, you'll use the NNI smoothing algorithm to reduce surface anomalies and create a more visually pleasing contour set:

1. If it's not still open from the previous exercise, open the SurfaceEdits_FINISHED.dwg or the SurfaceEdits_METRIC_FINISHED.dwg file.

2. In Prospector, expand the Surfaces ⇒ EG ⇒ Definition branches.

3. Right-click Edits and select the Smooth Surface option.

The Smooth Surface dialog opens.

4. Expand the Smoothing Methods branch, and verify that Natural Neighbor Interpolation is the Select Method value.

5. Expand the Point Interpolation/Extrapolation branch, and click in the Select Output Region value field.

6. Click the ellipsis button.

7. At the Select region or [rEctangle pOlygon Surface]: prompt, pick the rectangle located in the center of the surface for smoothing and then press to return to the Smooth Surface dialog.

8. Enter 5 for the Grid X-Spacing and Grid Y-Spacing values (for metric users, enter 2 for both values), and then press .

Note that Civil 3D will tell you how many points you are adding to the surface immediately below this input area by the value given in the Number Of Output Points field as shown in Figure 4.35. It's grayed out, but it does change on the basis of your input values.

Figure 4.35 Smooth Surface dialog

9. Click OK and the surface will be smoothed, similar to what is shown in Figure 4.36.

Figure 4.36 Surface before NNI smoothing (left) and after (right)

When this exercise is complete, you may close the drawing. A saved finished copy of this drawing is available from the book's web page with the filename SurfaceSmoothing_FINISHED.dwg or SurfaceSmoothing_METRIC_FINISHED.dwg.

Note that we said the surface will be smoothed — not the contours. Contour smoothing will be discussed later. To see the result of the surface smoothing, change Surface Style to Contours And Points to display your image as shown in Figure 4.37.

Figure 4.37 Points added via NNI surface smoothing

Note all of the points with a circle cross symbol. These points are all new, created by the NNI surface-smoothing operation. The derived points are part of your surface, and the contours reflect the updated surface information.

Surface Simplifying

Because of the increasing use in land development projects of GIS and other data-heavy inputs, it's critical that Civil 3D users know how to simplify the surfaces produced from these sources. In this exercise, you'll simplify the surface created from a drawing earlier in this chapter.

1. Open the SurfaceSimplifying.dwg file (or the SurfaceSimplifying_METRIC.dwg file). For reference, the surface statistics of the EG-GIS surface are shown in Figure 4.38.

Figure 4.38 EG-GIS surface statistics before simplification

2. In Prospector, expand Surfaces ⇒ EG-GIS ⇒ Definition.

3. Right-click Edits and select the Simplify Surface option to launch the Simplify Surface dialog.

4. Select the Point Removal radio button, as shown in Figure 4.39, and click Next to move to the Region Options page.

Figure 4.39 The Simplify Surface – Simplify Methods page

5. Accept the Region Options defaults as shown in Figure 4.40 and click Next to move to the Reduction Options page.

Figure 4.40 The Simplify Surface – Region Options page

6. Set Percentage Of Points To Remove to 20 percent and then deselect the Maximum Change In Elevation option.

This value is the maximum change allowed between the surface elevation at any point before or after the simplify process has run.

7. Click Apply.

The program will process this calculation and display a Total Points Removed number, as shown in Figure 4.41. You can adjust the slider or toggle on the Maximum Change In Elevation button to experiment with different values. Note that every time you click Apply or Finished, the number of points decreases by that percentage.

Figure 4.41 The Simplify Surface – Reduction Options page

8. Click Finish to close the wizard and fully commit to the Simplify edit.

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A Word about the Simplify Build Operation

Notice that the Simplify build operation is listed twice in the preview area of Prospector under Edits. This is because the command was run once when you clicked Apply and a second time when you clicked Finished. If you only want to run the Simplify Surface command once, you should click Apply and then click Cancel or just click Finished without clicking Apply first.

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When this exercise is complete, you may close the drawing. A saved finished copy of this drawing is available from the book's web page with the filename SurfaceSimplifying FINISHED.dwg or SurfaceSimplifying_METRIC_FINISHED.dwg.

A quick visit to the Surface Properties Statistics tab shows that the number of points has been reduced, as shown in Figure 4.42. On something like an aerial topography or DEM, reducing the point count probably will not reduce the usability of the surface, but this simple point reduction will decrease the file size. Remember, you can always delete the edit or deselect the operation on the Definition tab of the Surface Properties dialog to “un-simplify” the surface.

Figure 4.42 EG-GIS surface statistics after simplification

The creation of a surface is merely the starting point. Once you have a TIN to work with, you have a number of ways to view the data using analysis tools and varying styles.

Surface Analysis

Once a surface is created, you can display information in a number of ways. The most common so far has been contours and triangles, but those are the basics. By using varying styles, you can show a large amount of data with one single surface. Surface styles are discussed further in Chapter 21, “Object Styles.” While some of the styles are used for generating plans (such as contours), others lend themselves to analyzing the surface during creation.

For a surface object in plan view, Points, Triangles, Border, Major Contour, Minor Contour, User Contours, and Gridded are standard components and are controlled like any other object component. Directions, Elevations, Slopes, and Slope Arrows components are unique to surface styles. Note that the Layer, Color, and Linetype fields are grayed out for these components. Each of these components has its own special coloring schemes, which we'll look at in the next section. In this section, you will explore the elevation and slope analysis styles.

Elevation Banding

Displaying surface information as bands of color is one of the most common display methods for engineers looking to make a high-impact view of the site. Elevations are a critical part of the site design process, and understanding how a site varies in terms of elevation is an important part of making the best design. Elevation analysis typically falls into two categories: showing bands of information on the basis of pure distribution of linear scales or displaying a lesser number of bands to show some critical information about the site. In this first exercise, you'll use a standard style to illustrate elevation distribution along with a prebuilt color scheme that works well for presentations:

1. Open the SurfaceAnalysis.dwg file (or the SurfaceAnalysis_METRIC.dwg file).

2. Select the surface on your screen to activate the contextual tab.

3. From the TIN Surface contextual tab ⇒ Modify panel, choose the Surface Properties option.

The Surface Properties dialog appears.

4. On the Information tab, change the Surface Style field to Elevation Banding (3D).

5. Switch to the Analysis tab for the Elevations analysis type.

6. Verify that Create Ranges By is set to Number Of Ranges and that the value is set to 3, and then click the Run Analysis arrow in the middle of the dialog to populate the Range Details area.

7. Click OK to close the Surface Properties dialog.

Notice that only the border is currently showing since the surface is being shown in plan view.

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[-][Top][2D Wireframe]

You may have noticed three pieces of text in the upper-left corner of your model space. If you left-click on one of these In-Canvas View Controls, you will find that they are drop-down lists that you can use to change what you are looking at.

The first set of bracketed text will either be [-] (denoting that one viewport is being displayed) or [+] (if two viewports are being displayed).

The second set of bracketed text is the View Control and will list the current view within the brackets.

The third set of bracketed text is the Visual Style Control and will list the current visual style within the brackets.

All of these commands can also be changed from the View tab. If the Level Of Detail is currently active, an additional small icon will appear below this line of text.

These three pieces of text provide valuable information for easy reference while you work.

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8. From the View Control, select SW Isometric.

9. Zoom in if necessary to get a better view of the surface.

10. From the Visual Style Control, select the Conceptual option to see a semi-rendered view that should look something like Figure 4.43.

Figure 4.43 Conceptual view of the site with the Elevation Banding style

Save and keep the drawing open for the next portion of the exercise.

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AutoCAD Visual Styles

The triangles seen are part of the view style and can be modified via the Visual Styles Manager. Turning the Edge mode off will leave you with a nicely gradated view of your site. You can edit the visual style by clicking the Visual Style Control at the upper left of your drawing screen. You can also access the Visual Style Manager on the View tab ⇒ Visual Styles panel by clicking the small arrow in the lower-right corner of the panel. The Visual Styles Manager is shown here:

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You'll use a 2D elevation to clearly illustrate portions of the site that cannot be developed. Next, you'll manually tweak the colors and elevation ranges on the basis of design constraints from outside the program:

11. Click the View Control and select Top.

12. Click the Visual Style Control and select 2D Wireframe.

This site has a limitation placed in that no development can go below the elevation of 790′ (or 240 m). Your analysis will show you the areas that are below 790′ (or 240 m), a buffer zone to 791′ (or 241 m), and then everything above that.

13. Select the surface by clicking on the border. Right-click and choose the Surface Properties option.

The Surface Properties dialog appears.

14. On the Information tab, change the Surface Style field to Elevation Banding (2D).

15. On the Analysis tab, change Maximum Elevation for ID 1 and Minimum Elevation for ID 2 both to 790 (or 240 for metric users).

16. Change Maximum Elevation for ID 2 and Minimum Elevation for ID 3 both to 791 (or 241 for metric users).

17. Modify your Color Scheme to match Figure 4.44 by double-clicking on each color to open the Select Color dialog, selecting the appropriate color, and clicking OK to close the dialog. (The colors are red, yellow, and green from top to bottom, respectively.)

Figure 4.44 The Surface Properties dialog after manual editing

18. Click OK to accept the settings in the Surface Properties dialog.

When this exercise is complete, you may close the drawing. A saved finished copy of this drawing is available from the book's web page with the filename SurfaceAnalysis_FINISHED.dwg or SurfaceAnalysis_METRIC_FINISHED.dwg.

Understanding surfaces from a vertical direction is helpful, but many times the slopes are just as important. In the next section, you'll take a look at using the slope analysis tools in Civil 3D.

Slopes and Slope Arrows

Beyond the bands of color that show elevation differences in your models, you also have tools that display slope information about your surfaces. This analysis can be useful in checking for drainage concerns, meeting accessibility requirements, or adhering to zoning constraints. Slope is typically shown as areas of color similar to the elevation banding or as colored arrows that indicate the downhill direction and slope. In this exercise, you'll look at a proposed site grading surface and run the two slope analysis tools:

1. Open the SlopeAnalysis.dwg file (or the SlopeAnalysis_METRIC.dwg file).

2. Select the surface on your screen to activate the contextual tab.

3. From the TIN Surface contextual tab ⇒ Modify panel, choose Surface Properties.

The Surface Properties dialog appears.

4. On the Information tab, change the Surface Style field to Slope Banding (2D).

5. Switch to the Analysis tab of the Surface Properties dialog.

6. Choose Slopes from the Analysis Type drop-down list.

7. Verify that the Number field in the Ranges area is set to 3 and click the Run Analysis arrow in the middle of the dialog to populate the Range Details area.

The Range Details area will populate. You could change the minimums and maximums as you did in the previous exercise, but this time you'll keep the defaults.

8. Click OK to close the dialog.

Save and keep the drawing open for the next portion of the exercise.

The colors are nice to look at, but they don't mean much, and slopes don't have any inherent information that can be portrayed by color association. To make more sense of this analysis, you'll add a legend table:

9. Select the surface again, and on the TIN Surface contextual tab ⇒ Labels & Tables panel, choose Add Legend.

10. At the Enter table type [Directions Elevations Slopes slopeArrows Contours Usercontours Watersheds]: prompt, enter S to select Slopes.

11. At the Behavior [Dynamic Static]: <Dynamic> prompt, press again to accept the default value of a Dynamic legend.

12. At the Select upper left corner: prompt, pick a point on screen to draw the legend, as shown in Figure 4.45.

Figure 4.45 The Slopes legend table

Save and keep the drawing open for the next portion of the exercise.

By including a legend, you can make sense of the information presented in this view. Because you know what the slopes are, you can also see which way they go.

13. Select the surface, and on the TIN Surface contextual tab ⇒ Modify panel, choose Surface Properties.

The Surface Properties dialog appears.

14. On the Information tab, change the Surface Style field to Slope Arrows.

15. Switch to the Analysis tab of the Surface Properties dialog.

16. Choose Slope Arrows from the Analysis Type drop-down list.

17. Verify that the Number field in the Ranges area is set to 3 and click the Run Analysis arrow in the middle of the dialog to populate the Range Details area.

18. Click OK to close the dialog.

The benefit of arrows is in looking for “birdbath” areas that will collect water. These arrows can also verify that inlets are in the right location, as shown in Figure 4.46. Look for arrows pointing to the proposed drainage locations and you'll have a simple design-verification tool.

Figure 4.46 Slope arrows pointing to a proposed inlet location

When this exercise is complete, you may close the drawing. A saved finished copy of this drawing is available from the book's web page with the filename SlopeAnalysis_FINISHED.dwg or SlopeAnalysis_METRIC_FINISHED.dwg.

With these simple analysis tools, you can show a client the areas of their site that meet their constraints. Visually strong and simple to produce, this is the kind of information that a 3D model makes available. Beyond the basic information that can be represented in a single surface, Civil 3D also contains a number of tools for comparing surfaces. You'll compare this existing ground surface to a proposed grading plan in the next section.

Visibility Checker

The Zone of Visual Influence tool allows you to explore what-if scenarios. In this example, a 40′ (12 m) tower has been proposed for the site. A concerned neighbor wants to make sure that it won't obstruct their scenic view. You want to check it from the proposed surface:

1. Open VisibilityCheck.dwg or VisibilityCheck_METRIC.dwg.

2. In Prospector, expand the Surfaces branch, right-click on the FG surface, and choose the Select option.

3. On the TIN Surface contextual tab ⇒ Analyze panel, choose Visibility Check ⇒ Zone Of Visual Influence.

4. At the Specify location of object: prompt, using the Intersection Osnap select the center of the proposed tower located on the southern portion of the site (denoted by a large white square with an X inside).

5. At the Specify height of object: prompt, enter 40 to set the tower height to 40′ (metric users, enter 12 ).

6. At the Specify the radius of vision extent: prompt, pan to and select the endpoint at the upper-right corner of the cyan colored house located at the northeastern corner of the site.

Save and keep the drawing open for the next portion of the exercise.

The drawing now has bands of color:

• Green near the tower location indicates that the object is completely visible.
• Yellow indicates that the object is partially visible.
• Red indicates that the object is not visible.

So in our example, the homeowner on the upper right will be happy to know that the proposed 40′ tower will not appear in their view.

The next portion of the example will use the Point to Point tool.

7. Using the same drawing, zoom to the intersection of Syrah Way and Cabernet Court, where you will see a car driving on the right-hand side of the road.

We want to check the sight distance.

8. If it is not already selected, select the FG surface.

9. On the TIN Surface contextual tab ⇒ Analyze panel, choose Visibility Check ⇒ Point to Point.

10. At the Specify height of eye: prompt, enter 3.5 (metric users enter 1 ).

This sets the height of the driver's eye while sitting in a typical car.

11. At the Specify location of eye: prompt, click where the driver would normally be seated in the vehicle.

12. At the Specify height of target: prompt, enter 6 (metric users enter 1.8 ).

A rubber-banding sightline ray appears.

13. Click along the path where oncoming cars would be seen.

A sightline arrow is drawn on the screen:

• If the arrow is green, it means that the view is unobstructed and the command line will tell you the distance from the eye.
• If any portion of the arrow is red, it indicates that the view is obstructed, and the command line will tell you the distance at which the obstruction occurs.

When this exercise is complete, you may close the drawing. A saved finished copy of this drawing is available from the book's web page with the filename SurfaceVisibility_FINISHED.dwg or SurfaceVisibility_METRIC_FINISHED.dwg.

Unfortunately, these visual tools are not dynamic; if you change the surface, you will need to rerun the visual tools. Perhaps this will be addressed in a future release.

Comparing Surfaces

Earthwork is a major part of almost every land development project. The money involved with earthmoving is a large part of the budget, and for this reason, minimizing this impact is a critical part of the final design. Civil 3D contains a number of surface analysis tools designed to help in this effort, and you'll look at them in this section. First, a simple comparison provides feedback about the volumetric difference, and then a more detailed approach enables you to perform an analysis on this difference.

For years, civil engineers have performed earthwork using a section methodology. Sections were taken at some interval, and a plot was made of both the original surface and the proposed surface. Comparing adjacent sections and multiplying by the distance between them yields an end-area method of volumes that is generally considered acceptable. The main problem with this methodology is that it ignores the surfaces in the areas between sections. These areas could include areas of major change, introducing some level of error. In spite of this limitation, this method worked well with hand calculations, trading some accuracy for ease and speed.

With the advent of full-surface modeling, more precise methods became available. By analyzing both the existing and proposed surfaces, a volume calculation can be performed that is as good as the two surfaces. At every TIN vertex in both surfaces, a distance is measured vertically to the other surface. These delta amounts can then be used to create a third dynamic surface called a volume surface, which represents the difference between the two original surfaces.

TIN Volume Surface

Using the volume utility for initial design checking is helpful, but quite often contractors and other outside users want to see more information about the grading and earthwork for their own uses. This requirement typically falls into two categories: a cut-fill analysis showing colors or contours or a grid of cut-fill tick marks.

Color cut-fill maps are helpful when reviewing your site for the locations of movement. Some sites have areas of better material or can have areas where the cost of cut is prohibitive (such as rock). In this exercise, you'll use two of the surface analysis methods to look at the areas for cut-fill on your site:

1. Open the VolumeSurface.dwg or the VolumeSurface_METRIC.dwg file.

2. From the Analyze tab ⇒ Volumes And Materials panel, choose the Volumes Dashboard tool to display Panorama open to the Volumes Dashboard tab.

3. Click the Create New Volume Surface button to display the Create Surface dialog.

Notice that Type is already set to TIN Volume Surface. You also have the option to select Grid Volume Surface.

4. Change the name to VOL-EG-FG and set the style to Elevation Banding (2D).

5. Click the <Base Surface> field next to Base Surface to display the ellipsis button; once it's visible, click the ellipsis to select the EG surface.

6. Click the <Comparison Surface> next to Comparison Surface to display the ellipsis button; once it's visible, click the ellipsis to select the FG surface.

The Create Surface dialog should now look similar to Figure 4.47.

Figure 4.47 Creating a volume surface

7. Click OK to accept the settings in the Create Surface dialog.

Civil 3D will calculate the volume (Figure 4.48).

Figure 4.48 Composite volume calculated

Note that you can scroll right and left in Panorama to display additional information, including the ability to apply a cut or fill factor by typing directly into the cells for these values.

This new volume surface appears in Prospector's Surfaces collection, but notice that the icon is slightly different, showing two surfaces stacked on each other. The color mapping currently shown is just a default set, though, and does not indicate much.

8. Leave the Panorama open and in Prospector, expand the Surfaces ⇒ FG ⇒ Definition branches.

9. Right-click Edits and select the Raise/Lower Surface option.

10. Enter –0.25 at the command line to drop the site 3″ (metric users enter –0.075).

Notice that a yellow exclamation point status flag has appeared next to the volume surface in Panorama as well as in Prospector. The Panorama no longer lists the volumes and instead states “Out of date.”

11. Right-click the VOL-EG-FG surface in Panorama or Prospector and select the Rebuild option.

12. In Prospector under the Definition branch of the FG surface, click Edits and right-click the Raise/Lower edit in the preview area and select Delete.

13. A dialog will appear warning you that the selected definition will be permanently removed from the surface. Click OK.

14. Return to Panorama and rebuild the volume surface again to return to the original volume calculation.

15. Close Panorama when complete.

16. In Prospector, right-click VOL-EG-FG in the Surfaces branch and select the Surface Properties option.

The Surface Properties dialog appears.

17. In the Surface Properties dialog, switch to the Statistics tab and expand the Volume branch.

The value shown for the Net Volume (Unadjusted) is the same as shown in the Panorama in the first part of this exercise.

18. In the Surface Properties dialog, switch to the Analysis tab for the Elevations analysis type.

19. Verify that the Create Ranges By is set to Number Of Ranges and that the value is set to 3; then click the Run Analysis arrow in the middle of the dialog to populate the Range Of Details area.

20. Change Maximum Elevation for ID 1 and Minimum Elevation for ID 2 to -0.5 (or -0.15 for metric users).

21. Change Maximum Elevation for ID 2 and Minimum Elevation for ID 3 to 0.5 (or 0.15 for metric users).

22. Modify your Color Scheme to match Figure 4.49.

Figure 4.49 Elevation analysis settings for earthworks

The recommended colors are red, yellow, and green, where red indicates the worst case cut, green represents the worst case fill, and yellow represents a balance.

23. Click OK to close the Surface Properties dialog.

Save and keep the drawing open for the next portion of the exercise.

The volume surface now indicates areas of cut, fill, and areas near balancing, similar to Figure 4.50. If you leave a small range near the balance line, you can more clearly see the areas that are being left nearly undisturbed.

Figure 4.50 Completed elevation analysis

To show where large amounts of cut or fill could incur additional cost (such as compaction or excavation protection), you would simply modify the analysis range as required.

The Elevation Banding surface is great for onscreen analysis, but the color fills make it hard to plot or use in many applications. In these steps, you use the Contour Analysis tool to prepare cut-fill contours in these same colors:

24. In Prospector, right-click VOL-EG-FG in the Surfaces branch and select the Surface Properties option to display the Surface Properties dialog again.

25. On the Analysis tab, choose Contours from the Analysis Type drop-down list.

26. Verify that the Number field in the Ranges area is set to 3 and click the Run Analysis arrow in the middle of the dialog to populate the Range Details area.

27. Change the ranges to match those you entered in the previous portion of the exercise (as shown in Figure 4.49).

28. In the Major Contour column, click the small button to the far right to display the AutoCAD Select Color dialog and set a color for each ID.

Typical contour colors are

• Shades of red for cut
• A yellow for the balance line
• Shades of green for fill

29. Switch to the Information tab on the Surface Properties dialog, and change the Surface Style to Contours 1′ and 5′ (Design) or Contours 0.2 m and 1.0 m (Design).

30. Click the down arrow next to the Style field and select the Copy Current Selection option.

The Surface Style Editor appears.

31. On the Information tab, change the Name field to Contours 1′ and 5′ (Earthwork) or Contours 0.2 m and 1.0 m (Earthwork).

32. On the Contours tab, expand the Contour Ranges branch.

33. Change the value of the Use Color Scheme property to True.

It's safe to ignore the values here because you hard-coded the values in your surface properties.

34. Click OK to close the Surface Style Editor and click OK again to close the Surface Properties dialog.

When this exercise is complete, you may close the drawing. A saved finished copy of this drawing is available from the book's web page with the filename VolumeSurface_FINISHED.dwg or VolumeSurface_METRIC_FINISHED.dwg.

The volume surface can now be analyzed on a lot-by-lot basis or labeled using the surface-labeling functions to show the depths of cut and fill, which you'll look at in the next sections.

Labeling the Surface

Once the three-dimensional surface model has been created, it is time to communicate the model's information in various formats. This includes labeling contours, creating legends for the analysis you've created, adding spot labels, or labeling the slope. These exercises work through these main labeling requirements and building styles for each.

Contour Labeling

The most common requirement is to place labels on surface-generated contours. In Land Desktop, this was one of the last steps because a change to a surface required erasing and replacing all the labels. Once labels have been placed, their styles can be modified.

Contour labels in Civil 3D are created by special lines that understand their relationship with the surface. Everywhere one of these lines crosses a contour line, a label is placed. This label's appearance is based on the style applied and can be a major, minor, or user-defined contour label. Each label can have styles selected independently, so using some AutoCAD selection techniques can be crucial to maintaining uniformity across a surface. In this exercise, you'll add labels to your surface and explore the interaction of contour label lines and the labels themselves.

1. Open the SurfaceLabeling.dwg or Surface Labeling_METRIC.dwg file.

2. Select the EG surface in the drawing to display the TIN Surface contextual tab.

3. From the TIN Surface contextual tab ⇒ Labels & Tables panel, choose Add Labels ⇒ Contour – Single.

4. Pick any spot on a major contour to add a label.

5. Press when complete and press Esc to deselect the surface.

6. From the Annotate tab ⇒ Labels & Tables panel, choose Add Labels ⇒ Surface ⇒ Contour – Multiple.

7. Pick a point to the west of the site and then a second point across the site to the south of the site, crossing a number of contours in the process.

8. Press to end the picking.

9. From the Annotate tab ⇒ Labels & Tables panel, click on the Add Labels button instead of the drop-down to display the Add Labels dialog.

10. Set Feature to Surface and Label Type to Contour – Multiple At Interval.

11. Click the Add button.

12. Pick a point to the west of the site and then a second point across the site to the north of the site.

13. Enter 200 (for metric 60) at the command line for an interval value.

Save and keep the drawing open for the next portion of the exercise.

You've now labeled your site in three ways to get contour labels in a number of different locations. You will need additional labels in the northeast and southwest to complete the labeling, because you did not cross these contour objects with your contour label line. You can add more labels by clicking Add, but you can also use the labels created already to fill in these missing areas. By modifying the contour line labels, you can manipulate the label locations and add new labels. Next, you'll fill in the labeling to the northeast:

14. Zoom to the northeast portion of the site, and notice that some of the contours are labeled only along the boundary or not at all, as shown in Figure 4.51.

Figure 4.51 Contour labels applied

15. Zoom in to any contour label placed using the Contour – Multiple At Interval button, and pick the text.

Three grips will appear. The original contour label lines are quite apparent, but in reality, every label has a hidden label line beneath it.

16. Grab the northernmost grip and drag across an adjacent contour northeast of the original label, as shown in Figure 4.52.

Figure 4.52 Grip-editing a contour label line

New labels will appear everywhere your dragged line now crosses a contour.

17. Drop the grip somewhere to create labels as desired. Be sure to press Esc a few times when you are done labeling the contours to end the command.

Save and keep the drawing open for the next portion of the exercise.

By using the created label lines instead of adding new ones, you'll find it easier to manage the layout of your labels.

Surface Point Labels

In every site, there are points that fall off the contour line but are critical. In an existing surface, this can be the low point in a swale or a driveway that has to be matched. When you're working with a paper set of plans, the spot grade is the most common review element. One of the most time-consuming issues in land development is the preparation of grading plans with hundreds of individual spot grades. Every time a site grading scheme changes, these were typically updated manually, leaving lots of opportunities for error.

With Civil 3D's surface modeling, spot labels are dynamic and react to changes in the underlying surface. By using surface labels instead of points or text callouts, you can generate a grading plan early on in the design process and begin the process of creating sheets. In this section, you'll label surface slopes in a couple of ways, create a single spot label for critical information, and conclude by creating a grid of labels similar to many estimation software packages.

Labeling Slopes

Beyond the specific grade at any single point, most grading plans use slope labels to indicate some level of trend across a site or drainage area. Civil 3D can generate the following two slope labels:

In this next exercise, you'll apply both types of slope labels, and then look at a minor style modification that is commonly requested:

1. Using the drawing from the previous portion of the exercise, select the surface to display the TIN Surface contextual tab.

2. From the TIN Surface contextual tab ⇒ Labels & Tables panel, choose Add Labels ⇒ Surface ⇒ Slope.

3. At the Create Slope Labels or [One-point Two-point]: <One-point> prompt, press to select the default one-point label style.

4. Zoom in on the circle drawn on the western portion of the site and use a Center Osnap to place a label at its center, similar to that shown in Figure 4.53.

Figure 4.53 A one-point slope label

5. Press Esc or to exit the command.

6. From the TIN Surface contextual tab ⇒ Labels & Tables panel, choose Add Labels ⇒ Slope.

7. At the Create Slope Labels or [One-point Two-point]: <One-point> prompt, enter T to switch to a two-point label style.

8. Pan to the central portion of the site, and use an Endpoint Osnap to pick the left end of the line.

9. Use an Endpoint Osnap to select the right end of the line to complete the label.

10. Press Esc or to exit the command and view the label, as shown in Figure 4.54.

Figure 4.54 A two-point slope label

This second label indicates the average slope of the property. By using a two-point label, you get a better understanding of the trend, as opposed to a specific point.

When this exercise is complete, you may close the drawing. A saved finished copy of this drawing is available from the book's web page with the filename SurfaceLabeling_FINISHED.dwg or SurfaceLabeling_METRIC_FINISHED.dwg.

Critical Points

A typical grading plan is a sea of critical points that drive the site topography. In the past, much of this labeling and point work was done by creating coordinate geometry (COGO) points and simply displaying their properties. Although this is effective, it has two distinct disadvantages. First, these points are not reflective of the design but part of the design. This makes the sheet creation a part of the grading process, not a parallel process. Second, the addition of COGO points to any drawing and project when they're not truly needed just weighs down the design model. Point management is a mentally intensive task, and anything that can limit extraneous data is worth investigating.

Surface labels react dynamically to the surface and to the point of insertion. Moving any of these labels would update the information to reflect the surface underneath. This relationship makes it possible for one user to place labels on a grading plan while the final surface is still in flux. A change in the proposed surface is reflected in an update from the project, and an updated sheet can be on the plotter in minutes.

Surface Grid Labels

Sometimes, more than a few points are requested. Estimation software typically creates a grid of point labels that can be easily reviewed or passed to a contractor for fieldwork. In this exercise, you'll use the volume surface you generated earlier in this chapter to create a set of surface labels that reflect this requirement:

1. Open the SurfaceVolumeSurface_FINISHED.dwg (or the SurfaceVolumeSurface_METRIC_FINISHED.dwg file).

2. From the Annotate tab ⇒ Labels & Tables panel, choose Add Labels ⇒ Surface ⇒ Spot Elevations On Grid.

3. At the Select a surface <or press enter key to select from list>: prompt, press to display the Select Surface dialog.

4. Select VOL-EG-FG and click OK.

5. At the Specify a grid basepoint: prompt, pick a point southwest of the surface to set a base point for the grid.

6. At the Grid rotation: prompt, enter 0 .

7. At the Grid X spacing: prompt, enter 25 (7 for metric users).

8. At the Grid Y spacing: prompt, enter 25 (7 for metric users).

9. At the Specify the upper right location for the grid: prompt, pick a point northeast of the surface to set the area for the labels.

10. Verify that the preview window encompasses the VOL-EG-FG surface and press at the command line to continue.

Wait a few moments as Civil 3D generates all the labels just specified. Your drawing should look similar to Figure 4.55.

Figure 4.55 Volume surface with grid labels

Labeling the grid is imprecise at best. Grid labeling ignores anything that might happen between the grid points, but it presents the surface data in a familiar way for engineers and contractors. By using the tools available and the underlying surface model, you can present information from one source in an almost infinite number of ways.

When this exercise is complete, you may close the drawing. A saved finished copy of this drawing is available from the book's web page with the filename SurfaceVolumeGridLabels_FINISHED.dwg or SurfaceVolumeGridLabels_METRIC_FINISHED.dwg.

Point Cloud Surfaces

A point cloud is a huge bunch of 3D points, usually collected by laser scanner or Light Detection and Ranging (LiDAR). In a geographic information system (GIS), point clouds are often used as a source for a Digital Elevation Model (DEM). The technology has gotten less expensive and more accurate over the last few years, allowing LiDAR to quickly take over from traditional methods of collecting photogrammetry data.

Point clouds in many formats can be imported to Civil 3D. The most common format is the Log ASCII Standard (LAS) file. This binary format is a public format and at minimum contains x, y, and z data. LAS data can also include the following:

• Coordinate system of scanned area.
• Color — true color on RGB format.
• Intensity; LiDAR depends on lasers bouncing off objects and back to the scanning device and the intensity refers to the strength of the returned information. This value directly relates to the material from which the laser is bouncing. For example, concrete will have a stronger intensity than grass.
• Classification, which will be a number, most frequently between 0 and 9, that categorizes points based on material (i.e., ground, vegetation, or buildings).

For more information on the LAS standard, visit www.asprs.org.

Civil 3D can import a point cloud and use it in several ways. For instance, a laser scan of a bridge can be imported and placed for reference when designing a road through an existing abutment. In the example that follows, you will convert LiDAR data into a Civil 3D surface. It is important to note that point clouds often contain millions of points and require a beefy computer (and a little patience on your part) to process.

Importing a Point Cloud

A typical point cloud contains millions of points. These large files are kept external to Civil 3D in a point cloud database. After the LAS has been imported, the data is passed to three files: PRMD, IATI, and ISD. The ISD file contains the points themselves and is the only file needed by CAD if the point cloud would need to be re-created or used in base AutoCAD. By default these files get created in the same directory as the DWG but can be changed when importing the information.

If the point cloud you are working with contains coordinate system information (as all the examples in this book do), the software will automatically convert the point cloud to the units and coordinate system of the drawing. For the exercises in this chapter, it does not matter whether you choose the Metric or the Imperial template.

Civil 3D may take a long time to process these files, and you must ensure you have sufficient disk space to store them, as you will find in the following exercise. It is also a good idea to close the software and then reopen it to help clear some memory before starting memory-intensive tasks such as working with point clouds. The following exercise will show you how to import and work with a point cloud:

1. Start a new file by using the default Civil 3D template of your choice. Save the file before proceeding as PointCloud.dwg.

2. For Imperial users, set the Coordinate System to UTM Zone 17, NAD83, US Foot (UTM83-17F). For metric users, set the Coordinate System to UTM Zone 17, NAD83, Meters (UTM83-17).

3. In Prospector, right-click the Point Clouds branch and select the Create Point Cloud option to display the Create Point Cloud wizard, shown in Figure 4.56.

Figure 4.56 Create Point Cloud – Information page

4. Set the name of the point cloud to Serpent Mound.

5. Set the Point Cloud Style to Elevation Ranges, as shown in Figure 4.56, and click the Next button.

The Source Data page is displayed, as shown in Figure 4.57.

Figure 4.57 The Create Point Cloud – Source Data page

6. Using the white plus sign, browse to the Serpent Mound.las file (both Imperial and metric users can use this file).

Remember, all data and drawing files for this book can be downloaded from www.sybex.com/go/masteringcivil3d2013.

This is a large (90 MB) file containing roughly 1.4 million points and may require a minute or two to process.

7. Click the Next button to display the Summary page, as shown in Figure 4.58.

Figure 4.58 The Create Point Cloud – Summary page

8. Accept the defaults as shown in Figure 4.58 and click Finish to process the point cloud.

9. If the New Point Cloud Database – Processing In Background dialog appears, click Close to dismiss it.

You may notice a pop-up message in the lower-right corner of your screen indicating that the Point Cloud database is being created in the background.

10. Once the point cloud is created, it will disappear and a new pop-up message will appear stating that the point cloud has been created and a link is provided that says Click Here To Zoom. Click this link.

When complete, a portion of a bounding box outlining a portion of the point cloud is displayed in the center of the screen. Save the drawing but leave it open to complete the next exercise.

Working with Point Clouds

Once the point cloud is visible in your drawing, you'll want to follow a few rules of thumb to prevent performance problems. The key-in POINTCLOUDDENSITY value controls what percentage of the full point cloud displays on the screen at once. You can also access this value using a slider bar in the Point Cloud contextual tab. However, it is easier to hit the percentage you want on the first try if you use the key-in value. The lower this value, the fewer points are visible; hence the easier it will be to navigate your drawing. The POINTCLOUDDENSITY value does not have any effect on the number of points used when generating a surface model (this is similar to the Level Of Detail value used to aid surface processing).

When you are changing view directions on a point cloud, we recommend that you use preset views and named views to flip around the object. The orbit commands should not be used, as they are a surefire way to max out your computer's RAM. If you used the default template, your surface will be located on the V-SITE-SCAN layer. We suggest that you freeze the layer if you do not need to see the point cloud. Use Freeze instead of Off for layer management so the point cloud is not accounted for during pan, zoom, and regen operations (this is true for all AutoCAD objects, but it makes a huge difference when working with point clouds).

Creating a Point Cloud Surface

By specifying either an entire point cloud or a small region of a point cloud, you can create a new TIN surface in your drawing. Any changes to the point cloud object will render the surface definition out of date. In the following exercise, a new TIN surface is created from the point cloud previously imported:

1. Continue using the PointCloud.dwg file from the previous exercise.

2. Select the bounding box representing the point cloud to display the Point Cloud: Serpent Mound contextual tab, as shown in Figure 4.59.

Figure 4.59 The Point Cloud contextual tab

3. From the Point Cloud contextual tab ⇒ Point Cloud Tools panel, choose Add Points To Surface to display the Add Points To Surface wizard, as shown in Figure 4.60.

Figure 4.60 The Add Points To Surface – Surface Options page

4. Name the surface Serpent Mound South. Leave the style set to the default.

5. Click Next and the Region Options page is displayed, as shown in Figure 4.61.

Figure 4.61 The Add Points To Surface – Region Options page

6. Choose the Window radio button, and click Define Region In Drawing.

7. Define the region by creating a window around the southern half of the point cloud.

8. Click Next to see the Summary page, as shown in Figure 4.62, and click the Finish button.

Figure 4.62 The Add Points To Surface – Summary page

When this exercise is complete, you may close the drawing. Due to the large file size, a finished state of this drawing is not available for download.

The Bottom Line