Bridging GPS Gaps in Urban Canyons: The Benefits of ZUPTs

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Abstract
Land-based mobile mapping systems operate in urban environments, where losses of GPS lock occur, leading to often extended periods of free-navigation mode. The result is degraded navigation accuracy. Performing periodic ZUPTs (zero velocity updates) enables calibration of velocity error sources, leading to a lower positioning error rate as compared with unaided navigation mode. This paper presents a study of the impact of ZUPTs on navigation accuracy in urban canyons, with special emphasis on the speed and reliability of ambiguity resolution supported by periodic ZUPTs. An analysis of the positioning errors after ZUPT events versus unaided and GPS/inertial navigation system (INS) results is also presented. In addition, the observability aspects of static INS calibration are briefly addressed. The results discussed here are based on investigation of a high-accuracy, tightly integrated GPS/INS system providing georeferencing to a fully digital imaging component, designed for near-real-time highway mapping.

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