Geodetski Vestnik (Jan 2005)
Določitev absolutnega položaja GPS-sprejemnika iz kodnih opazovanj : Absolute GPS Positioning from Code Observations
Abstract
In the article we present the single point positioning procedures from pseudoranges for obtaining the absolute position of the GPS antenna and its clock offset. First we define the direct and iterative solutions from four or more pseudoranges, further we derive a solution from three pseudoranges used in situations with obstructions to the receiver-to-satellite line of sights, for example in vehicle navigation (altitude hold mode). We present the theoretic demonstration of preferences of each method and discuss the geometric conditions leading from several solutions to the most likely one. The main purpose of this study is finding the optimal computation method to attain a well-based initial solution guess for the recursive method of computation – Kalman filtering, and to obtain quality apriori values for further carrier-phase processing. In order to achieve a well-grounded method comparison in the Matlab R14 program, we apply all methods on the same set of observation data and in connection with broadcast ephemerides considering troposphere refraction models and Earth aberration. Additional analyses show that the number of satellites and observation time interval have a significant effect on the accuracy improvement.
