Geoida Help

Convert points between projection types

Question: How do I convert point coordinates between two different projection types, for example from MGA94 Transverse Mercator in Zone 55, to VICGRID94 Lambert's Conformal Conic projection coordinates?

Answer: Conversion of coordinate data requires firstly that both the 'source' projection and the 'target' projection have been defined, and that a suitable 'transformation' has been defined to convert between the source system and the target system. Check for these in the Definition menu Projection and Transformations options or in the List Definitions option.

The conversion or transformation required will fit one of these two situations:

1. Both systems are on the same datum - point conversion
2. Different datums - transformation

Case 1 can be achieved with a simple Zone-to-Zone transformation. Case 2 may be more complex with multiple steps and require the aquisition of suitable transformation parameters between the two datums and require working with geographic coordinates.

With respect to the question at hand, the first situation applies and a simple Zone-to-Zone transformation will achieve the conversion. If required, set up a new Zone-to-Zone transformation from MGA94 Zone 55 to VICGRID94 (no zone number), and with the FROM Datum and TO Datum both set to GDA94. Note that the direction of the conversion is not important as Geoida will select the required direction depending on which system is the source and which is the target. Application of the conversion may be made in any of the following options in the Points menu:

• During importation of point data - Import
• Apply to exported data - List Points / Export
• Whole job - Transform Job

Note that in the Select Transformation window (see Transform Job) within any of these options, only transformations that match the current job settings will be listed. Refer also to Coordinate-type conversion in Job Configuration.