Shown Table 1. A Map of GPS observation points Table 1. The number of combinations of satellite with the number of satellite. We apply static positioning or rapid static positioning belong to relative positioning to observe the same time everyday, and altitude of receiver is 15 degree. Accuracy is estimated as comparison of dimension of absolute observed error, and relative accuracy of distance X, and Y by relative positioning with 2 GPS receivers.
Received data is calculated by the method of least squares according to computer process.
Allowable scope error limits absolute observed error to 5mm, and relative accuracy is shown Table 2. In the case of more than 7, the time of observation needs over 30min within 1km, 60min within 2.5km, and 120min within 10km. In case of 4 of satellite, the time of observation needs over 20min within 1km. This research calculates dimension of observed error followed satellite combination in distance to determine least observed time of baseline classified followed GPS satellite combinations, and To get optimum observed time suited to fiducial point survey, the conclusions was taken as below by static positioning, and rapid static positioning. When static positioning, and rapid static positioning belong to relative positioning were used, economic observed time to get sufficient data within sphere of critical allowable error came to reduced phenomenon by increasing the number of satellites or reducing length of base line when combined satellites.