(
GPS terminology)
The process of determining the relative difference in position between two marks This can be done with a much greater precision than absolute, single point positioning. A receiver (antenna) is placed over each spot and measurements are made by observing the same satellites with each receiver at exactly the same observation interval and with overlapping times . This technique allows the cancellation (during computations) of all errors that are common to both receivers. These include satellite clock errors, propagation delays, etc.