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On the Maps in the LO system you will find the positive X axis to the south and the positive Y-axis to the west. This is a left-handed Cartesian co-ordinate system, whilst the
computer thinks in a right-handed system. For the display of gridded data just use the normal co-ordinate system but be careful with the grids origin. Some software allows taking
care of this by giving a negative central scale factor.
There are some topographical map sheets floating around in UTM (Datum not specified) and Lambert Conformal (Clarke 1880) projections.
The Geological Survey of Namibia believes that the research and development undertaken by Prof. C. Merry provide the most accurate parameters. Therefore some original notes:
The datum transformation parameters I have supplied are based upon 13 Doppler points, of which the DMA used a subset of 3. The RMS fit for these 13 points is 3m, which means there
may be some parts of the country where the discrepancy is 10m (this is an indication of the accuracy of the original terrestrial survey, carried out some 100 years ago).
The map projection is a modified transverse mercator, with a false origin and units of legal
meters. The plane co-ordinates would need to be converted to international
meters and
the (int. meters) co-ordinates of the false origin added. Then the standard transverse Mercator equations can be used to convert the plane co-ordinates to geographical (int.
meter values for the modified Bessel ellipsoid: a=6377483.m).
The geographical co-ordinates would be converted to X, Y, Z Cartesian co-ordinates (using a=6377483..m), and the datum shifts added, with appropriate sign.
These transformed Cartesian co-ordinates are converted to WGS84 geographical co-ordinates, using the WGS84 ellipsoid parameters.
A few additional comments:
Prof. Merry sells Windows software to do these conversions (US$150).
My understanding is that the military UTM maps use the modified Bessel ellipsoid, with international
meters, not the WGS84 ellipsoid; but I could be wrong.
The difference between international meters
and legal meters is fairly small. As far as I know, all practicing
surveyors and engineers use instruments (tapes,
EDM, GPS)
calibrated in international meters and solve for a scale factor (sometimes not even this, when working in small areas) when tying their surveys to the national
control network.
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