GPS World - May 2008 - (Page 33)

Vehicle Integration | AVIONICS & TRANSPORTATION were mounted on survey tripods instead of being worn by people. The adjacent photo shows the tripods with the P-units during the 10-foot channel test. The engineer is standing by the AutoDOCS reference point and the wireless remote unit is the white ball on the car roof. The low-profile PAS antenna is not visible. For each ped channel distance, the car started from a stop at the start line and drove at a maximum of 10 mph through the ped channel while staying centered on the parking lot line (visible in the photo) that was the center of the channels. The car then looped around to repeat the trial, five trials per channel. The V-unit in the car collected the data. The data analysis consisted of comparing the differential positions determined by PAS to AutoDOCS. Since the PAS measurements were relative to the P-units and AutoDOCS measurements were relative to its reference point, the measurements had to be normalized. The antennas were aligned with the center line of the car and the distance between them was accurately measured. However, accurate velocity as the car moves is needed. AutoDOCS as delivered to NHTSA does not output the unneeded velocity measurements so the PAS standalone velocity was used to estimate the vector resulting in a normalization error of up to 10 centimeters in the results. Combined with the 2-centimeter kinematic error margin, the truth accuracy is still an order of magnitude less than carrier-smoothed differential CA-code performance. FIGURE 6 shows the plot of the kinematic carrier (blue) and PAS (black) differential positions normalized relative to a P-unit. The larger errors near the start point and the end of the channel are about at the same north coordinate as two large metal refuse bins alongside the course. The consistent performance of the kinematic carrier DGPS system shows it has much higher immunity to multipath. FIGURE 7 shows the horizontal differential position and velocity error with HDOP versus time for the trial shown in Figure 6. Average position error was 1.29 meters with a 1-sigma of 0.65 meters. Velocity www.gpsworld.com averaged 0.36 meters/second error with a 1-sigma of 0.22 meters/second. Velocity truth came from standalone V-unit receiver so these errors are not precise. HDOP was consistent with an average of 2.53. FIGURE 8 shows that the Kalman filter residuals for that trial were good with an average of 8 millimeters. TABLE 1 provides a summary of all the trials and data points. Position Error - Avg [m] Position Error - Std [m] Position Error - Min [m] Position Error - Max [m] Velocity Error - Avg [m/s] Velocity Error - Std [m/s] HDOP Avg HDOP Max Number of Points 1.55 0.73 0.16 3.80 0.36 0.27 2.78 56.23 3255 Å TABLE 1 Summary of all DGPS test trials O M N I S T A R H I G H P E R F O R M A N C E TM D G P S : BRINGING DECIMETER ACCURACY WITHIN REACH Introducing OmniSTAR High Performance (HP), our revolutionary new DGPS system that redefines the standard for differential correction. OmniSTAR has developed cost-effective, reliable real-time corrections enabling high-accuracy applications over entire continents without deploying local base stations. Our innovative HP signal provides five times the accuracy of standard DGPS for horizontal accuracy of ~ +/- 10-15 cms. HP means a wide-area solution offering previously unobtainable levels of accuracy, opening the door for high-precision uses such as auto steering, guidance and automation of agri-vehicles, increased hit probability for GIS/utilities, rough grading for construction applications, survey projects, oil exploration, aerial photogrammetry, and more. We just raised the bar on accuracy and reliability, but it ' s way within your reach. OmniSTAR HP. Others promise Ð we deliver. © 2005, OmniSTAR Contact us for more information www.omnistar.com ® Expect high performance May 2008 | GPS World 33 http://www.omnistar.com http://www.omnistar.com http://www.gpsworld.com

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GPS World - May 2008

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