Global Positioning System Survey - Long Session

The Global Positioning System (GPS)is one example of many Global Satellite Navigation Systems (GNSS) that provide extremely precise (~1cm) positioning relative to the Earth Ellipsoid. The Earth Ellipsoid is a mathematically well defined surface that, on average, best fits the form of the Earth (approximated by an ellipsoid of rotation).

In the GSVS, long session (24 hours or more) GPS results are used to precisely locate the bench marks relative to the Earth Ellipsoid, providing latitude, longitude, and ellipsoidal height (height above or below the Earth Ellipsoid). This information is used to both locate the various survey instruments (for numerous location dependent corrections) and serves to determine the distance between bench marks when calculating geoid slopes (the "run" in "rise over run").