These corrections are radioed to the remote, or rover, receiver which must then be capable of applying these individual corrections to each satellite used in the position solution. A line of sight along the ground is no longer necessary for very precise surveying. Positions can be measured up to 30 km from a reference point without intermediate points. In order to correctly estimate the number of signal wavelengths at the reference and remote receivers, they must be close enough to insure natural disturbances in the signal wavelength are not too great. This usually means that carrier-phase GPS measurements must be taken with a remote and reference station within about 30 kilometers of each other.
Special software is required to work with the carrier-phase differential measurements.
The costs of receivers vary depending on capabilities. Other costs include the cost of multiple receivers when needed, post-processing software, and the cost of specially trained personnel. Many of the small hand held units allow positions and routes to be downloaded to GIS software and geological mapping and GIS packages. Small units can generally store 100 to 300 positions and perhaps dozen of routes. We can categorize GPS equipment and tasks into four groups.