Taken together, the Clarke 1866
reference ellipsoid and the geoid origin of Meades Ranch
comprimise the North American Datum of 1927 (NAD27)
However, since the advent of satellite geodesy, large errors have been encountered when comparing the results of today's highly accurate survey techniques with the NAD27 values
To remedy this, a new reference ellipsoid, the Geodetic Reference System
(GRS), was recommended by the International Geodesy
and subsequently adopted by the National Geodetic Survey
, creating the North American Dantum of 1983 (NAD83)
When to use:
- NAD27: if you are in N. America, and want to match your NAD27 topo maps.
- NAD83: if you are in N. America, and are collecting raw data.
- WGS84: if you are going to compare with GPS data you have collected elsewhere in the world.