All that is needed is a custom datum to convert the local datum (Cape) to
WGS84 upon which the Haartebeesthoek 94 datum is based.
What was done below was to modify the MAPINFOW.PRJ file coordinate system
parameters already supplied with MapInfo 5.0 for South Africa, and insert a
custom datum clause with the information gleaned from some documentation
taken from here:
http://w3sli.wcape.gov.za/surveys/MAPPING/WGS84.HTM.
The projection is still Transverse Mercator (Gauss-Kruger).
According to the documentation above, to convert from Cape (local datum) to
Haartebeesthoek 94 (WGS84), using the Bursa-Wolfe method MapInfo uses, the
parameters are:
Shift X: -134.73
Shift Y: -110.92
Shift Z: -292.66
Rotation x: 0
Rotation y: 0
Rotation z: 0
Scale Factor: 1
Prime Meridian: 0
I've included both sets of entries for the mapinfow.prj file for either the
Haartebeesthoek 94 or Cape datums
"--- South African Projections Clarke 1880 Cape---"
"Albers Equal-Area 18/32 South", 9, 19, 7, 23, -23, -18, -32, 0, 0
"Lambert Conformal Conic ", 3, 19, 7, 23, -23, -18, -32, 0, 0
"Gauss-Kruger LO 17", 8, 19, 7, 17, 0, 1, 0, 0
"Gauss-Kruger LO 19", 8, 19, 7, 19, 0, 1, 0, 0
"LO19 with offset", 8, 19, 7, 19, 0, 1, 0, 3700000
"Gauss-Kruger LO 21", 8, 19, 7, 21, 0, 1, 0, 0
"Gauss-Kruger LO 23", 8, 19, 7, 23, 0, 1, 0, 0
"Gauss-Kruger LO 25", 8, 19, 7, 25, 0, 1, 0, 0
"Gauss-Kruger LO 27", 8, 19, 7, 27, 0, 1, 0, 0
"Gauss-Kruger LO 29", 8, 19, 7, 29, 0, 1, 0, 0
"Gauss-Kruger LO 31", 8, 19, 7, 31, 0, 1, 0, 0
"---South African Projections Haartebeesthoek 94---"
"Albers Equal-Area 18/32 South (Haartebeesthoek 94)", 9, 9999, 28, -134.73,
-110.92, -292.66, 0, 0, 0, 1, 0, 7, 23, -23, -18, -32, 0, 0
"Lambert Conformal Conic (Haartebeesthoek 94)", 3, 9999, 28, -134.73,
-110.92, -292.66, 0, 0, 0, 1, 0, 7, 23, -23, -18, -32, 0, 0
"Gauss-Kruger LO 17 (Haartebeesthoek 94)", 8, 9999, 28, -134.73, -110.92,
-292.66, 0, 0, 0, 1, 0, 7, 17, 0, 1, 0, 0
"Gauss-Kruger LO 19 (Haartebeesthoek 94)", 8, 9999, 28, -134.73, -110.92,
-292.66, 0, 0, 0, 1, 0, 7, 19, 0, 1, 0, 0
"LO19 with offset (Haartebeesthoek 94)", 8, 9999, 28, -134.73, -110.92,
-292.66, 0, 0, 0, 1, 0,, 7, 19, 0, 1, 0, 3700000
"Gauss-Kruger LO 21 (Haartebeesthoek 94)", 8, 9999, 28, -134.73, -110.92,
-292.66, 0, 0, 0, 1, 0, 7, 21, 0, 1, 0, 0
"Gauss-Kruger LO 23 (Haartebeesthoek 94)", 8, 9999, 28, -134.73, -110.92,
-292.66, 0, 0, 0, 1, 0, 7, 23, 0, 1, 0, 0
"Gauss-Kruger LO 25 (Haartebeesthoek 94)", 8, 9999, 28, -134.73, -110.92,
-292.66, 0, 0, 0, 1, 0, 7, 25, 0, 1, 0, 0
"Gauss-Kruger LO 27 (Haartebeesthoek 94)", 8, 9999, 28, -134.73, -110.92,
-292.66, 0, 0, 0, 1, 0, 7, 27, 0, 1, 0, 0
"Gauss-Kruger LO 29 (Haartebeesthoek 94)", 8, 9999, 28, -134.73, -110.92,
-292.66, 0, 0, 0, 1, 0, 7, 29, 0, 1, 0, 0
"Gauss-Kruger LO 31 (Haartebeesthoek 94)", 8, 9999, 28, -134.73, -110.92,
-292.66, 0, 0, 0, 1, 0, 7, 31, 0, 1, 0, 0
Regards,
-Bill
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