As you know, the Global Positioning System (GPS) helps us to determine the global position of a vehicle with the help of GPS satellites. The latitude and longitude of the vehicle can be calculated from the GPS data. The accuracy of GPS can vary with the type of sensor; some sensors have an error range of within a few meters, and some have one within less than a meter. We can find vehicle state by combining GPS, Inertial Measurement Unit (IMU), and wheel odometer data and by using the sensor fusion algorithms. This can give a better estimate of the vehicle. Let's look at the position estimation modules used for the DARPA Challenge 2007.

The POS LV modules from Applanix are the modules used in the Stanford autonomous car called Junior. They are a combination of GPS, IMU, and wheel encoders or Distance Measurement Indicator (DMI). You can find them at http://www.applanix.com/products/poslv.htm.

The OxTS module is another GPS/IMU combo module from Oxford Technical Solution (OxTS) (http://www.oxts.com/). This module was extensively used in the DARPA Challenge in 2007. The module is from the RT 3000 v2 family (http://www.oxts.com/products/rt3000-family/). The entire range of GPS modules from OxTS can be found at http://www.oxts.com/industry/automotive-testing/.