The performance of GPS standard positioning service without selective availability

The accuracy of the Standard Positioning Service of GPS has greatly improved after the termination of Selective Availability. Based on GPS observations from permanent GPS-fixed stations, the actual accuracy of GPS without SA is analyzed. For Station NCTU, the local geodetic coordinates are computed with the C/A code pseudo-ranges, and then transformed into a local grid system with Trans-Mercator projection. From 77984 single epoch observations collected in twenty-nine days, the 95% accuracy is found to be ΔE : 17.6544m, ΔN : 11.8236m, ΔH : 31.8018m. For five selected UNAVCO stations, the axes of error ellipsoid are computed.