A deformation monitoring system includes a data recording and control center, one or more base receivers with associated antennas that have a substantially unrestricted view of the sky and acquire and track satellite signals used for global positioning and slave receivers at various locations over the site being monitored, the slave receivers also acquiring and tracking the satellite signals. The system processes range information provided by the slave receivers over an extended period of time to determine the positions of the respective slave receivers. In this way, the precise positions of the respective slave receivers can be calculated, even if the slave receivers are able to observe and collect data from one or more satellites for only three or four relatively short time intervals at various sky positions during the extended period.