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Using inertially-aided real-time kinematic technology as a land-based mapping tool
The photograph in figure 3 shows an aerial view of King Street, and graphically illustrates the advantages of using the POS LV in an urban canyon environment. Figure 1 shows the same area as seen from the mapping vehicle and clearly shows why GPS reception would be difficult to maintain in this area. Equipped with the POS LV system the vehicle was driven under normal data capture conditions and at traffic speed along King Street. The planned mission utilized the fully integrated POS LV/IARTK configuration. The blue line on the photograph was generated using the post-processed position and orientation solution, which places the vehicle in a best-estimated location. The yellow dots show the positional information derived using a single stand-alone Differential GPS solution from the same test mission.  Figure 3. King Street The 1 Hz stand-alone DGPS position solution, indicated by the yellow dots, can be seen to wander substantially off track, when compared to the blue line generated by the 200 Hz POS LV solution. The effect of GPS satellite dropout and multipath, caused by the tall buildings, is readily apparent in the results obtained with the stand-alone DGPS solution. The solution generated using the POS LV system (blue line) shows a significant improvement in position (in addition to precise orientation data) accuracy despite the identical GPS lockout and multipath effects. Figure 4 shows an aerial view of the Gardiner Expressway, with the POS LV blue line data correctly positioned on Lakeshore Boulevard under the expressway. GPS reception was intermittent and often non-existent along Lakeshore Boulevard, with the result that a corresponding DGPS solution was unavailable in places.  Figure 4. Lakeshore boulevard The mapping vehicle was driven along the road beneath the expressway with the POS LV/IARTK configuration in operation. The data was post-processed using the Applanix POSPac software. An accurate position and orientation solution was obtained by processing the aided inertial data in both forward and reverse directions, placing the vehicle in its true estimated position, despite a complete absence of GPS reception in most locations. The stand-alone DGPS solution generated substantial position errors, and a total lack of DGPS data can be seen at the south west edge of Lakeshore Boulevard. In contrast, the DGPS data on the north side of the expressway was generated by the mapping vehicle traveling on the Gardiner Expressway at the end of the demonstration and virtually mirrors the POS LV data, illustrating that full GPS reception was available. From the results obtained during the Toronto mobile mapping demonstration, it is apparent that a stand-alone DGPS system cannot provide reliable or in fact useful position data in environments that compromise GPS reception. |