What is WGS84 and what is the difference between WGS84 and NAD83?
WGS84 (World Geodetic System 1984) is a spatial reference system that was created to be used solely by the Global Positioning System (GPS). From 1986 to 1994, WGS84 was considered the same as NAD83. Both were based on the same Doppler reference frame and were therefore compatible with each other, at least to the accuracy of the Doppler reference frame (about a meter). It was not uncommon for the datum to be called “NAD83/WGS84”. Compared to the ITRF, it turns out that “NAD83/WGS84” was mis-scaled, its origin was offset and its axes were misaligned resulting in a coordinate shift in Canada of 1 to 1.5 m. Since GPS played a major role in refining the ITRF, it made practical sense that the GPS reference frame be truly geocentric and aligned with ITRF. And so on Jan 2, 1994, WGS84 was realigned to ITRF91 and was no longer compatible with NAD83. This new realization of WGS84 was called WGS84(G730) and could now be called “ITRF/WGS84”. The total coordinate difference between WGS84(G730) and
