[Proj] Help with a custom projection that is Transverse Mercator with Affine post-process

Mikael Rittri Mikael.Rittri at carmenta.com
Tue Jan 29 04:02:37 EST 2013

Hello James.
Just a partial answer, I am afraid:

I don't think you can add an affine post-processing to a Proj.4 CRS definition.

For your example, the interpretation of the MapInfo CoordSys clause should be

"CoordSys Earth Projection", // Just a name (probably the wrong one in this case)
8,                   // The projection type, in this case Transverse Mercator
33,                 // The geodetic datum, in this case GRS80 (treat it like WGS84)
7,                   // length unit, in this case meter
117,                // central longitude
0,                   // central latitude
0.9996,           // scale factor
500000,          // false easting
10000000,       // false northing
7,                   // length unit for affine transformation, also meters,
0.890953, -0.455062, 2903977.24, 0.455063, 0.890954, -6919253.68,         // affine parameters A, B, C, D, E, F
-100000, -100000, 100000, 100000               // bounds

I think the basic CRS in this example can be expressed in Proj.4 as


which gives GDA94 / MGA zone 50, but I think you must implement the affine transformation yourself.

I got the information from http://www.sgsi.com/dnld/MapInfoPro_UserGuide_Current.pdf
but I didn't understand the meaning of the affine parameters.

And I think the 8 ought to have been 3008, maybe...

Best regards,

Mikael Rittri
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