This section will provide a brief generalised overview, in
point form, of the development of horizontal datums from 1966 -2000.
The Australian Geodetic Datum (AGD) produces a single datum for
Australian using the Australian National Spheroid (ANS).
The Australian Map Grid (AMG) is derived from UTM map projection of latitude and
longitudes on the AGD.
The Australian Geodetic Datum 1996 (AGD66) results from the network adjustment of geodetic
observations to 1996. The co-ordinate set comprises the AGD66, is based on the ANS.
UTM projection of AGD66 co-ordinates, using the ANS, gives the Australian Map Grid 1966
(AMG66)
By 1982, deficiencies were shown to exist in the AGD66 and the new adjustment, the
Geodetic Model of Australia 1982 (GMA82), and the co-ordinate set from this adjustment was
adopted as the Australian Geodetic Datum 1984 (AGD84). This is based on the ANS. AGD84
geographical co-ordinates differ from AGD66 co-ordinates from 2m in SE Australia to about
5m NW, but the variation is not uniform
The Australian Map Grid 1984 (AMG84) eastings and northings are derived from AGD84
geographical co-ordinates using the UTM projection from ANS.
The Geodetic Reference System 1980 (GRS80) is the global reference spheroid adopted by the
IAG in 1980.
The World Geodetic System 1984 (WGS84) is currently used for GPS satellite navigation
systems. The parameters of the WGS84 spheroid are nearly identical to those for the GRS80
spheroid
The ICSM resolved in 1988 to adopt the new Geocentric Datum of Australia (GDA), which will
be implemented by 1st January 2000. GDA is intended to supersede the AGD66 and
AGD84 and lead to a homogeneous national co-ordinate datum for future mapping.
The Map Grid of Australia (MGA) will be used to display GDA geographical co-ordinates and
will therefore supersede AMG4 and AMG66.
The MGA is UTM projection of the GDA geographical co-ordinates using Redfern’s
formulae with the geometrical constants of GRS80. The resultant change in map grid
co-ordinates corresponds to a NE horizontal shift of approximately 194m to 207m.
The move to GDA will not effect the heights in Australia, i.e. AHD
Summary
Datum spheroid
map grid
AGD66
ANS
AMG66
AGD84
ANS
AMG84
GDA94
GRS80
MGA94
GDA2000
GRS80
MGA2000
