Dilution of Precision Computation Procedure When Measuring Receiver Position in Geodetic Coordinates.
NAVAL SURFACE WEAPONS CENTER DAHLGREN VA
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Certain users of the Global Positioning System GPS use the geodetic coordinate system to define their receiver position. Satellite positions, computed from either ephemeris or almanac data, are best stated, however, in terms of Earth-centered, Earth-fixed ECEF cartesian coordinates. This presents a problem when computing values for a dilution of precision DOP in position-- the measure by which the four satellites most suitable for range measurements are determined. Before receiving transmissions from GPS satellites and using them to determine precise receiver position, the user must determine which four satellites are in the configuration that will maximize system accuracy. This is accomplished by computing a DOP value for all groups for four satellites that are in view. For GPS users who measure their receiver position in geodetic coordinates, this value should reflect the use of these coordinates, rather than ECEF cartesian coordinates. This report outlines five algorithms, all used in the process of computing a DOP in position. The method to compute satellite position is described assuming the user is using almanac data, and the dilution of precision in position term is defined in terms of geodetic coordinates. The expressions defined for DOP are for users at sea level, measuring receiver position in Earth-fixed, geodetic coordinates. Keywords Geometric dilution of precision GDOP
- Navigation and Guidance