Transformation of Coordinates

Coordinate transformation is the process of changing coordinates from one reference frame or datum to another: for example, from GDA94 to GDA2020 or GDA94 to AGD66.

Transformation products and tools

The ICSM website contains extensive information about transforming coordinates between Australian datums and international reference frames. The resources range from explanatory fact sheets describing a coordinate transformation in conceptual terms right through to tools such as an online transformation service and downloadable software.

The Geocentric Datum of Australia 2020 Technical Manual defines and describes the preferred methods to transform coordinates between GDA94 and GDA2020, and GDA94 to AGD66, as well as how to apply AUSGeoid. The GDA94 Technical Manual v2.4 has further background on how and why GDA94 was established and additional transformations between AGD66 and GDA94.

The application of a block shift, determined from one or more common points can be a convenient way of transforming coordinates where only a low level of transformation accuracy is required.

Low Accuracy GDA94 <> GDA2020 Transformation

An average block shift based on the coordinates of 5400 survey control marks distributed over the whole of Tasmania provides the following values for a coordinate transformation where the estimated maximum error of the actual transformation is 0.5 metres.

TO CONVERT	GDA94 to GDA2020
Eastings	Add 0.4m
Northings	Add 1.4m
Latitude	Subtract 0.047 sec
Longitude	Add 0.018 sec

Table 1: Approximate Block shift values for Tasmania - GDA94 to GDA2020

Low Accuracy AGD66 <> GDA94 Transformation

An average block shift based on the coordinates of 163 survey control marks distributed over the whole of Tasmania provides the following values for a coordinate transformation where the estimated maximum error of the actual transformation is 3 metres.