International Terrestrial Reference Frame
The Global Positioning System (WGS84) has been refined on several occasions since its inception and is now aligned with the International Terrestrial Reference Frame (ITRF) at the level of a few centimetres. For most people it is impossible to obtain a WGS84 position with an accuracy of better than a few metres, but it is now relatively easy to obtain ITRF positions with an accuracy of a few centimetres. (See AUSPOS - our free global GPS processing service). If accurate WGS84 positions are required, it is best to use ITRF positions.