Datum Change

A job can use a Local co-ordinate system with a user defined origin, or can be on a standard Datum and projection. Each datum is an ellipsoid fitted to the earth based on adjusted coordinates of many geodetic stations.

The Datums and projections are defined in a file usually called ‘MapProjections.csv’. having the map projections and Datums defined in a user changeable file allows users to enter their own local projections.

Transform to another Datum
This option transforms co-ordinates from the current Datum to the selected Datum using the transformation grid file. All the points in the job will be converted. You must supply the transformation grid file, which will be either an NTv2 format file (.gsb) or a US standard transformation grid file.

Click here to see the format of the MapProjections.csv file.
or here for info on how to set the Datum and Projection for a job.

Australia
A special transformation file in the NTv2 format has been provided for each state to perform the transformation between GDA and AGD. The conversion routine has been written by University of Melbourne and is called GDAit. It has been written by D.J. Mitchell and P.J. Collier.

You will need the GDAit.DLL in the same directory as your .EXE file.

You can obtain the current transformation files from the Government web site in your state. The LPI site in NSW has all grids.

http://www.lpi.nsw.gov.au/gda/cgi-bin/geod_download

For an explanation of Datums History, click here.