Dynamic Evaluation of High Accuracy Differential GPS

M. Sergi, B. Newstrom, A. Gorjestani, C. Shankwitz, M. Donath

Abstract:	Methods and results of experiments designed to quantify the dynamic performance (position accuracy and latency) of dual frequency, carrier phase RTK DGPS systems are presented. Latency is often ignored or assumed to be negligible, but this is not the case for high-speed vehiclebased applications. A latency of 20 milliseconds produces a direction of travel position error of 0.4 meters (15.8 inches) at a speed of 20m/s. When warning or crash avoidance systems are based on vehicle location, position errors in the longitudinal direction can lead to rear-end crashes and errors in the lateral direction can lead to lane departure crashes. In this paper, the Trimble MS750 receiver was tested using differential corrections from both Trimble MS750 and Leica SR530 conventional RTK base stations. The Trimble MS750 system was also tested using the Trimble Virtual Reference Station (VRS). The final system under test is the recently available NavCom SF-2050M which uses the NavCom StarFire™ worldwide differential GPS correction system. For the experiments described herein, the position solution accuracy of these DGPS systems was measured against ground truth using image processing techniques. To measure against ground truth, a high-resolution calibrated digital camera with an externally controlled shutter was mounted coaxially beneath the phase center of a DGPS antenna and pointed at the ground. A series of accurately positioned reference points were used to precisely position and align square tiles used as position references. As the test vehicle is driven over the tiles, the camera shutter is synchronized with the GPS pulse per second signal. If a tile is captured in the field of view of an image, the physical location of the antenna with respect to the tile can be determined from the camera calibration. The global position of the antenna at the time the shutter was triggered can be determined from the position of the tile in the image. The global physical location of the antenna determined in this manner is compared with the estimated position of the antenna as provided by the GPS receiver, providing an error measurement. Repeatedly driving over multiple tiles provides statistically relevant information regarding the error associated with the DGPS system.
Published in:	Proceedings of the 2003 National Technical Meeting of The Institute of Navigation January 22 - 24, 2003 Disneyland Paradise Pier Hotel Anaheim, CA
Pages:	581 - 592
Cite this article:	Sergi, M., Newstrom, B., Gorjestani, A., Shankwitz, C., Donath, M., "Dynamic Evaluation of High Accuracy Differential GPS," Proceedings of the 2003 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 2003, pp. 581-592.
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