Evaluation of in-vehicle GPS-based lane position sensing for preventing road departure

We present a systematic method for quantifying the dynamic performance of differential GPS, and in particular the Novatel RT-20 DGPS unit, for determining a vehicle's lateral position in a highway lane. Image processing is used. Novatel's RT-20 Double Differencing Carrier Phase Measurement System is specified to achieve real-time positioning performance of better then 20 cm nominal accuracy. This paper documents the results from a series of dynamic tests carried out on the RT-20 to verify its actual accuracy while on a moving vehicle. The approach adopted here incorporates synchronized data acquisition using two separate computer systems, and experimental verification of the computational latency of the RT-20. The image processing scheme used for this analysis achieved high accuracy by taking advantage of subpixel resolution in the image processing algorithm. Our results indicate that the RT-20 system exhibited a mean error of 2.03 cm in the lateral direction, and 3.16 cm in the longitudinal direction (note that both lateral and longitudinal are with respect to the moving truck) while moving at speeds ranging from 15 mph through 40 mph. The corresponding error standard deviations were 1.98 cm and 34.87 cm respectively. Our main interest is in the lateral positioning performance of the RT-20, which turns out to be very good. Furthermore, we believe that the longitudinal error standard deviation exhibited by the RT-20 can be reduced further by using an algorithm that eliminates the outlier data points.