What is the best method for achieving high absolute accuracy in a GPS survey?
A. All GPS surveys should be based on accurate recent coordinates, in the EtrS89 coordinate system, of regularly monitored, positionally stable geodetic monuments. The active and passive stations of the OS National GPS Network are ideal for this, and are freely available from this web site. Our active stations are continuously monitored on a daily basis and have ETRS89 coordinates with (typically) 5 mm horizontal accuracy. Our passive stations are monitored on a five year cyclic programme, and have ETRS89 coordinates with (typically) 5 cm horizontal accuracy (better for some stations). Using the National GPS Network reference stations, ETRS89 coordinates of your own primary survey stations, and hence of all your surveyed points, can be established using your usual GPS surveying methods. ETRS89 is the European standard precise GPS coordinate system, so your GPS survey will be consistent with thousands of other independent surveys throughout Europe. ETRS89 is in turn precisely related to
