GPS observation procedures
The satellite measurement technic works with meter accuracy worldwide. To achieve cm-accuracy differential methods are used. Both methods are shortly described in case of the GPS satellite system.
Global Positioning System (GPS)
Differential GPS (DGPS)
The accuracy of GPS may be increased considerably by including a reference station (GPS receiver on a site with known coordinates). In the so-called post-processing method, the observations of the rover (mobile GPS receiver) are then corrected so that, depending on the type of receiver, accuracies of a few decimeters or a few centimeters may be reached. This differential method may also be carried out in real time. Pre-requisite for this method is a communications link (radio, mobile phone / GSM, etc.) between the GPS reference station and the mobile user. Depending on the type of observations (code or carrier phase), the method is known as differential GPS (DGPS) with accuracies of a meter, or real-time kinematics (RTK) with accuracies up to centimeters.
With its product swipos, swisstopo offers such DGPS and RTK positioning services for all of Switzerland, therefore, making the use of personal reference stations obsolete.