Comparative Analysis of Static Differential GPS/GNSS Positioning Using Two and Three or More Receivers

摘要

Differential GPS/GNSS positioning gives accurate coordinates as well as positions of observed points on the earth surface. To obtain the accuracy as well as the reliability and the most probable positions of observed points using the post processing software that accompanies the receivers, least squares adjustment technique is applied. Applying least squares adjustment technique requires three or more receivers, that is two or more rovers and one base receiver to be used. Using three or more receivers makes the observation a closed loop observation. But in most cases where the number of points whose positions are to be determined is small, the observations are carried out with only two (rover and base) receivers. Using only two receivers (rover and base) implies that each of the points will be occupied one after the other with respect to the base receiver. In this, least squares adjustment cannot be applied as the observation is not a closed loop one, hence, the accuracy of the observations as well as those of the determined positions and the most probable positions of the observed points cannot be determined. Consequently, this study comparatively analyses the positions determined from static Differential GPS/GNSS observations using two and three or more receivers with a view to obtaining significant differences in the positions of observed points. A control station (ASPXW42A), two new points (ESO 1 and ESO 2), a base receiver and two rover receivers were used in the study. The positions of the new points were first determined with closed loop observation and then with opened loop observation. The two sets of observations were processed with compass post processing software. From the processing results, it was discovered that the reliability of the observations and those of the determined positions of the opened loop observation were not computed. The two sets of coordinates of the observed points were compared and their differences were used to compute the difference magnitudes. The computed difference magnitude of each point was compared with its corresponding 95% confidence level to determine if the difference between the two positions of each point is significant. The comparison results showed that there were significant differences in the positions. It is recommended that differential GPS/GNSS observation should be carried out with three or more receivers.