# Australian Map Grid

## Australian Map Grid (AMG66)

The least squares adjustment of the Australian geodetic network performed in March 1966 used the Australian Geodetic Datum. This adjustment produced a set of coordinates which, in the form of latitudes and longitudes, is known as the Australian Geodetic Datum 1966 coordinate set (AGD66).

The grid coordinates derived from a Universal Transverse Mercator (UTM) projection of the AGD66 coordinates, using the Australian National Spheroid, is now known as the Australian Map Grid 1966 coordinate set (AMG66).

## Universal Transverse Mercator (UTM)

The Transverse Mercator projection represents ellipsoidal positions (latitude & longitude) as grid coordinates (easting and northing) on a cylindrical surface, resulting in a number of zones. Uniform scale factor, false origins and zone size and numbering have been adopted for the Universal Transverse Mercator Projection.

## Australian Map Grid (AMG84)

In 1982 a new national adjustment, referred to as the Geodetic Model of Australia 1982 (GMA82), was performed using all data previously included in the 1966 adjustment as well as additional, modern terrestrial and space-based observations. This new adjustment also used the gazetted Australian Geodetic Datum. The coordinate set resulting from this adjustment was accepted by the National Mapping Council in 1984 and is known as the Australian Geodetic Datum 1984 (AGD84).

The equivalent Universal Transverse Mercator grid coordinates, projected using the Australian National Spheroid, are known as the Australian Map Grid 1984 (AMG84).

Coordinates on the AMG are derived from a Universal Transverse Mercator projection of latitudes and longitudes on the Australian Geodetic Datum (AGD), Parameters used for the AMG shown below.

Central scale factor: 0.9996 500,000 m 10,000,000 m 6 degrees 3 degrees 31 ANS a = 6,378,160 m 1/f = 298.25

Any Universal Transverse Mercator projection would use identical parameters except that the appropriate ellipsoid would be used (eg for UTM coordinates from WGS84 latitudes and longitudes were being projected the WGS84 ellipsoid would be used - semi-major axis 6378137.0 flattening = 1/298.257223563).

Redfearn's formulae are used to convert between latitude and longitude and Australian Map Grid (or Universal Transverse Mercator) coordinates (Redfearn 1948). These formulae are shown with worked examples in The Australian Geodetic Datum Technical Manual (National Mapping Council 1986).