Role of the Geometry in GPS Positioning

Abstract

`Bad geometry` of GPS positioning degrades the precision; this is expressed in a multiplier called DOP. There are some erroneous statements concerning DOP (every DOP value is always greater than 1; vertical DOP is always greater than the horizontal one; PDOP is inversely proportional to the volume of tetrahedron, etc.). One should treat the `mathematical` and the `geometrical` DOP differently: former is the square root of covariance matrix, latter is the reciprocal of the volume of a tetrahedron. For statistical analysis of DOP its values were calculated from computer generated satellite configurations. There are some illustrations (skyplots) demonstrating the simulation program of quasi GPS satellite configurations.