It is not generally known, however, that there are different GPS technologies giving any accuracy between the 20-metre and the millimetre range. Small hand-held receivers can produce decimetre accuracy when used in differential mode using carrier phase information and have proved very useful in heritage projects comprising large areas and for control point surveys for photogrammetric or satellite image processing. Range is computed by triangulation in the resulting triangle. For details see other CIPA Working Groups. Aerial Photogrammtry is a well established method of surveying and standardised to a large extent.
Larger scales are possible if devices like balloons or miniature aircraft are used.
Remote Sensing from satellites is a useful method in documentation comprising larger areas. The advent of systems with dramatically improved resolution is of great importance to cultural heritage documentation, especially where aerial photos are not available. Methods of Surveying in Archaeology Demonstrated at the Tang Emperors Mausoleums. Recording and Visualizing Topography and Object Geometry for Archaeological Documentation.