When you are importing data from a DWG or DXF file, layers within the file are assigned a Revit line weight based on the weight assigned to each layer. If the layer line weights are set to Default in the CAD file, they will follow a translation template you can configure in Revit that maps the layer colors to Revit line weights. To access these settings in Revit, select the Insert tab and click the shortcut arrow at the bottom right of the Import panel. This will open the Import Line Weights dialog box, shown in Figure 8.2.

Figure 8.2. Defining settings for imported DWG/DXF line weights

As you can see in the title bar of this dialog box, these settings are stored in a text file (TXT) in C:Program FilesAutodesk Revit Architecture 2011Data. There are several predefined text files based on international CAD standards for layer color:

Click the Load button to import one of these predefined line weight import templates or your own. Based on the unique needs of some projects, you might also consider creating customized import settings files and storing them along with the rest of your project data.

[Directories]
ImportLineweightsNameDWG=< Full path to TXT file >

You can bring CAD data into Revit in two ways: importing and linking. Each method has advantages and disadvantages.

After you have configured the necessary settings for inserted CAD data and decided on whether to import or link, you will need to understand certain options during the import/link process. We'll discuss the preferred settings for each of the options based on real-world situations in sections Importing 2D Data and Importing 3D Data. To place your first CAD file into a Revit project, switch to the Insert tab and select either Link CAD or Import CAD. No matter which tool you use, there will be several important options at the bottom of the command dialog box, as shown in Figure 8.3.

Figure 8.3. Options available for import/link

Let's examine the meaning of the settings in this situation:

Once you have data imported or linked into a Revit project, you have several ways of manipulating the data to suit your needs:

In this situation, we will assume that 2D CAD data will be linked into the Revit model to be converted into building elements. Although the positioning of the files is important, the color and line weights of the imported data are not.

To begin the next exercise, you will need the files c08-Plan01.dwg and c08-Start.rvt. You can download these files from this book's companion website: www.sybex.com/go/masteringrevit2011. After downloading, open the c08-Start.rvt file, and activate the Level 1 floor plan.

Linking Very Large CAD Data

Use caution when attempting to link or import CAD files with vector data very far from the origin. Revit has distance limitations on imported vector data that—if exceeded—may result in a warning, as shown here:

Notice in the warning message above that Revit will automatically use Center To Center positioning if the distance limitations are exceeded. This will preclude you from using the origin of the linked file for Origin To Origin placement. If you must link data that is physically larger than a twenty-mile cube—which may occur in projects such as airports or master plans—you should separate the data into smaller portions before linking. If the data is smaller than the twenty-mile cube but is located farther than twenty miles from its origin, an alternate origin should be coordinated with your project team, and the data should be moved closer to the origin.

If you need to use 2D CAD data as an integrated component of your team coordination, different settings become important. Examples of these types of scenarios might include the following:

Most of the settings and procedures for conversion apply to the coordination process; however, color and the placement visibility will be different. Because this data will be included in the output from Revit, you will always want the color option to be set to Black and White in the options during linking. It is also likely that some sort of background plans will be exported from the Revit model for use in coordination by one or more consultants using a CAD-based program. The data returned in this process may still contain the background information originally exported from Revit; thus, we recommend agreement to a standard that establishes unique layers for the consultants' content. This will help you select layers to be loaded when linking your consultants' files into the Revit project.

Use these options when linking CAD files into Revit for plan-based coordination:

If the Current View Only is not selected, the 2D CAD data will be visible in all other views. This could be a nuisance in views such as sections and elevations; however, you might find it useful to visualize the data alongside the Revit model, as shown in Figure 8.7.

Figure 8.7. Existing CAD data integrated with the Revit model

Your company's CAD detail library does not need to go to waste when you implement Revit. External CAD data can be linked into drafting views, allowing you to leverage the powerful view coordination tools within Revit. Entire sheets of CAD details can be inserted to reduce the number of linked files Revit has to reconcile; however, we recommend linking one detail into each drafting view and utilizing Revit's ability to automatically manage the view references with callouts, sections, and detail views. You may also want to name these drafting views with a unique prefix to help keep track of where any linked CAD data might reside. For example, a drafting view might be named CAD-Roof Detail 04. Also refer to Chapter 4, "Configuring Templates and Standards," for additional information on view organization.

In this exercise, you will create a drafting view into which a single CAD detail will be linked. This view can be referenced throughout your Revit model using a section, callout, or elevation view with the Reference Other View option selected in the Options Bar, as shown in Figure 8.8.

Figure 8.8. Creating a view as a reference to a drafting view

To begin this exercise, open the c08-Jenkins.rvt file. You can download this file and the associated CAD file (c08-Detail.dwg) from the book's companion website: www.sybex.com/go/masteringrevit2011.

In Chapter 9, "Advanced Modeling and Massing," you will learn more about harnessing the impressive modeling tool set in Revit's conceptual massing environment; however, the fast and flexible process of design may lead architects toward a tool in which they have more expertise or comfort. This type of massing design workflow is supported in Revit under the following conditions:

This example demonstrates the process of creating an in-place mass by linking an external model—in this case, a SketchUp model. You can download the file c08-Mass.skp from the book's companion website: www.sybex.com/go/masteringrevit2011.

Now that a new mass has been created, you can assign mass floors and begin to see calculated results in schedules of masses and mass floors. (Refer to Chapter 9 for more information on these processes.) Calculation of volumes, perimeters, and mass floor areas will work well in this workflow, but be careful when using imported model geometry with the By Face tools because face updates will likely be more difficult for Revit to maintain than with native Revit massing.

Using linking instead of importing enables continued iteration of the form in the original software. In the case of this example, you may edit the original file in Google SketchUp, which is available as a free download from http://sketchup.google.com, or you can download the file c08-Mass-2.skp from the book's companion web page.

If you modify and save the original SKP file yourself, save, close, and reopen the Revit project. Alternatively, open the Manage Links dialog box, select the SKP file, and click Reload. If you want to use the alternate file downloaded from the book's companion web page, use the following steps:

With the modified mass loaded, notice the changes in the Mass Schedule and Mass Floor Schedule.

Similar to the data as mass workflow, externally modeled data can be used as a driver for more complex forms. An example might be the need to generate a complex curved roof surface. We will demonstrate this workflow using Rhinoceros by McNeel (www.rhino3d.com) to generate a shape, link the shape into Revit, and create a roof by face on the shape.

As shown in Figure 8.10, a complex surface is generated in Rhino from drawing two curves and using the Extrude Curve Along Curve tool. Note that some reference geometry was exported from a Revit model to DWG and linked into this study in Rhino.

Figure 8.10. Curves for a complex surface in Rhino

A flat surface model is enough to generate a roof by face in Revit; however, it may be difficult to see the imported surface, so use the Extrude Surface tool to give it a thickness. Once the surface is complete (Figure 8.11), select only the double-curved geometry, choose File

Figure 8.11. Completed complex surface in Rhino

You can download the Rhino file (c08-Roof-Face.3dm) and SAT export (c08-Roof-Face.sat) from this book's companion web page. You can also download the sample Revit project and continue the process as follows:

The original shape can be edited in the originating software and will update in Revit via the link if the original exported SAT file is overwritten. To update the roof based on the newly modified massing geometry, select the roof and click the Update To Face button in the Modify | Roofs tab.

Figure 8.14. Completed roof with tops of walls attached

Yet another derivation of the reference data workflow supports the use of linked model geometry for specific instances of building components. Examples of this scenario might include a complex canopy structure being designed in SolidWorks or a building's structural framing being modeled in Bentley Structural Modeler. The workflow is again similar to that of using imported data as a mass or face; however, the file format will help you control the component's visualization in Revit. In the previous exercise, we used an SAT format to transfer complex curved geometry from Rhino to Revit; however, a limitation of an SAT file is that the geometry only contains one layer, making it impossible to vary material assignments for different components of the design. We recommend using a solids-based DWG, DGN, or DXF file format, which will maintain a layer structure in most cases.

In the following example, you will create an in-place structural framing component that will act as a placeholder for a consultant's structural model created in Bentley Structural Modeler. You will be using the file c08-Framing.dgn, which you can download from the book's companion web page: www.sybex.com/go/masteringrevit2011.

Switch to a 3D view, and you should see the entire contents of the DGN model (Figure 8.15). Because the linked content was created as a structural framing model, the linked data will be displayed similarly to any other structural framing element in Revit. Examine the linked model in different plans and sections to observe this behavior.

Figure 8.15. DGN structural model linked into Revit

Utilizing linked models in DWG, DGN, or DXF format also allows you to modify the graphic representation of the elements within Revit. To adjust these settings, do the following:

When you are using linked model data for custom components, the consistency of the data you bring into Revit from other programs depends on the ability of that software to generate organized information. Some programs utilize layers, and some don't. Recognizing this difference will give you the best opportunity for success in coordination through interoperability.

The first step to any export is to establish the set of files to be exported. The following steps will walk you through the process:

The subsequent steps in the exporting process are slightly different based on each export format. You will usually see a Save To Target dialog box that allows you to specify automatic or manual naming conventions for multiple exported files. Exporting FBX files or images simply requires a file location and name.

In addition to creating and maintaining lists of views for various exporting tasks, we recommend that you create at least one standardized layer mapping file for CAD format exports. Revit stores these settings in a text file (*.txt) that can be loaded from any location on your computer or network. To access the Export Layers settings, click the Application button and select Export

Figure 8.22. Accessing export layer settings on the DWG Properties tab

Several exporting templates based on the industry standard layering guidelines are included (Figure 8.23) with Revit Architecture and can be applied by clicking the Standard button in the Export Layers dialog box. Similarly to import settings, you may want to create customized layer export templates and save them with your project data for future reference. Note that export templates will inherit all layer names of linked CAD files in your active project. Because of this, we recommend saving a copy of your export templates in a zip archive in case you need to return to the original template.

Figure 8.23. Industry standard layering conventions can be applied to export settings.

Layer names and colors can be customized by directly editing the values within the Export Layers dialog box (Figure 8.24). Notice when a layer's color is modified, the color of all other layers of the same name will update automatically. Layers listed in bracketed italics—for example, {A-WALL-FULL}—are automatically referencing the layer assigned to a parent category. For example, in Figure 8.24, the Cut layer for the subcategory Wall Sweeps will adopt the same layer (A-WALL) as the parent category of Walls.

Figure 8.24. Exported layer names and colors can be customized for any standard.

Special layer suffixes can be assigned to Revit model objects that are subject to graphic overrides from phasing. The standard phasing overrides (Existing, Demolished, and Temporary) are listed as object styles in the Export Layers dialog box and can be customized as required. These settings are applied to the end of the specified layer for a given Revit object. For example, if a new wall was set to export to A-WALL, a wall displayed as demolished in a Revit view would be exported to the A-WALL-DEMO layer.

The following are the DWG settings for exporting:

Earlier in this chapter we discussed using Google SketchUp for conceptual building massing studies. These studies were imported directly into the Revit environment for further development of a true building information model. Revit model data can also be exported via 3D DWG to Google SketchUp, where visualization studies can be conducted on an entire project or even a simple wall section. In the following exercise, we will create a wall section study from Revit to Google SketchUp using files you can download from the book's companion website: www.sybex.com/go/masteringrevit2011.

Once the DWG model is loaded in Google SketchUp, you can use the Paint Bucket tool to apply materials to individual components, use the Push/Pull tool to hide or expose layers of the wall construction, and use the line tools to customize the profile of the revealed layers, as shown in Figure 8.29.

Figure 8.29. Completed wall study in Google SketchUp

According to Wikipedia, "Industry Foundation Classes (IFC) is a data model based on a neutral and open specification that is not controlled by a single software vendor or group of vendors. It is an object-oriented file format with a data model developed by the buildingSMART Alliance (International Alliance for Interoperability, IAI) to facilitate interoperability in the building industry." The IFC model specification is registered by the International Standards Organization (ISO) as ISO/PAS 16739 and is currently in the process of becoming the official International Standard ISO/IS 16739. Because of its focus on ease of interoperability between BIM software platforms, some government agencies are requiring IFC format deliverables for publicly funded building projects.

The use of IFC format in a Revit workflow can be useful if you understand its limitations. Some scenarios where IFC exchange may apply and facilitate data exchange include, but are not limited to, the following:

You can export the Revit model quite effectively to the IFC 2x2, 2x3 or BCA ePlan Check formats by clicking the Application button and selecting the Export menu. The resulting IFC file (Figure 8.30) can be viewed in a number of programs that can be downloaded at no cost from any of the following websites:

Figure 8.30. Revit model exported to IFC format

Importing IFC data into Revit is similar to the process for importing 3D CAD geometry; however, the data generated is intended to be more intelligent and editable. Although this method has great potential, the accuracy of Revit's IFC import is highly dependent on the software used to generate the IFC output. We recommend the use of one of the free IFC viewers listed previously to inspect IFC data prior to importing into a Revit project. (Note that only some tools, such as DDS CAD Viewer, have the ability to measure objects in an IFC format file.)

Once you've reviewed the contents of the IFC file, you can open it in Revit and integrate it into your coordination process as follows:

If an updated IFC file is received, repeat steps 1–3, and overwrite the RVT file created in step 3. When the host project file is reopened, the linked RVT file containing the imported IFC content will be updated.

3D Exports by Level

Effective coordination between Revit Architecture and AutoCAD MEP frequently relies on the exchange of 3D DWG files of limited scope with respect to the overall project. MEP engineers using AutoCAD MEP will usually manage their BIM with one model file per level. Even though the entire architectural model can be exported to a single DWG model, they may not be able to reference such a large model efficiently. The good news? Your Revit project can be set up to achieve this by creating 3D views with section boxes for each level.

Begin by creating a series of floor plans designed for exporting (discussed earlier in this chapter). In the View Range settings for these plans, set the Top value to Level Above, Offset: 0 and the Bottom value to Associated Level, Offset: 0. Create a 3D view for each level required in the project and rename the views according to your standards. In each duplicated 3D view, right-click the ViewCube and select Orient To View