Low-cost land vehicle attitude determination using single-epoch GPS data, MEMS-based inclinometer measurements

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GPS compasses equipped with short baselines can provide precise heading and elevation information for land vehicles. Most recent research in this area has focused on developing single-frequency, single-epoch ambiguity resolution, as the ambiguity resolution in a single epoch can guarantee total independence from carrier phase slips and lock losses. The reliability of single-frequency, single-epoch ambiguity resolution, however, are often insufficient for actual applications due to the weak baseline model. For land vehicle applications, baseline elevation can also be measured by inclinometer, which provides an important constraint that can be exploited to directly assist the ambiguity resolution process. In this study, we developed an innovative method that fully integrates MEMS-based inclinometer measurements into single-difference GPS observation equations and obtains the fixed baseline solution via weighted constrained integer least squares. We then explored the performance and effectiveness of the proposed method by building an integrated GPS/inclinometer compass system (IGICS) with low-cost GPS receivers (U-Blox LEA-6T) and a MEMS-based inclinometer (SCA-100T). Both actual static and dynamic experiments demonstrated that our method is capable of successfully fixing the set of integer ambiguities to the correct value for land vehicles equipped with very short baselines. The proposed method is also more easily implemented than the traditional augmenting scheme with rate gyros and IMU, as evidenced by a comparative experiment conducted using three approaches: (1) the new method; (2) horizontal constraint without inclinometer measurements; and (3) exploiting inclinometer measurements without imposing horizontal constraints.