Karl,
Central Meridians of 21°, 23°, 25°,and 27° East make sense
for the South African Survey Grid AS PUBLISHED BY THE
REPUBLIC OF BOTSWANA. (The scale factor at origin is
1.0 and NOT 0.9996).
Note that South and West are positive components.
***********************************************************
Goofy variants of the UTM standard military Grid do NOT
make sense whatsoever. I recommend that you inform
your client that is something to avoid like the plague.
Consider Zone 34.5 highly diseased ...
***********************************************************
The Clarke 1880 (modified) ellipsoid used for the
Cape Datum of 1950 has the following parameters:
a = 6,378,249.145 meters
b = 6,356,514.967 meters
Origin Point for the Datum is at Buffelsfontein, near
Port Elizabeth where:
Latitude = -33° 59' 32.000" South
Longitude = 25° 30' 44.622" East of Greenwich
The best published values from Cape 1950 Datum
to WGS 84 Datum for Botswana are:
ΔX = -135.8 meters ±0.6 meters,
ΔY = -103.8 meters ±0.6 meters,
ΔZ = -290.0 meters ±0.6 meters.
Prof. Clifford J. Mugnier ([EMAIL PROTECTED])
Surveying, Geodesy, & Photogrammetry
LOUISIANA STATE UNIVERSITY
2408 CEBA Building
Baton Rouge, LA 70803
Voice & Facsimile: (225) 578-8536
======================================
SEE: http://www.ASPRS.org/resources.html
http://www.ce.LSU.edu/~mugnier/
======================================
Hi,
I have a client that has set up a UTM projection for Botswana. He is unsure
if the projection/datum is correct though. Can anybody shed any insights? A
copy of his text is below. Thanks in advance for your help.
Karl
>I've set up a new class of UTM projections for the region of
>Botswana as follows:
>
>
>"--- Universal Transverse Mercator (Clarke 1880 Modified) ---"
>"UTM Zone 34, Southern Hemisphere (Clarke 1880 Modified)", 8, 19, 7, 21, 0,
>0.9996, 500000, 10000000
>"UTM Zone 35, Southern Hemisphere (Clarke 1880 Modified)", 8, 19, 7, 27, 0,
>0.9996, 500000, 10000000
>"UTM Zone 34.5, Southern Hemisphere (Clarke 1880 Modified)", 8, 19, 7, 24,
>0, 0.9996, 500000, 10000000
>
>These are all calling the CAPE datum (no. 19) but I can seem to find where
>I can check this in MapInfo. That is, I'd like to check the parameters of
>the Cape datum itself as being used by MapInfo. Page 516 of the MapInfo
>Users' Guide (version 5.0) Appendix H says that the CAPE datum is based on
>a Clarke 1880 ellipsoid. Well, this is more or less correct, although the
>CAPE datum is supposed to be based on a Clarke 1880 MODIFIED ellipsoid. I
>belive the appropriate ellipsoid is the Clarke 1880 (modified for ARC) as
>per Page 530 (Appendix I) of the same MapInfo Users' Guide.
>
>I'd like to think that the CAPE datum no. 19 is actually calling for the
>Clarke 1880 (modified for ARC) ellipsoid, but is there a way to
>double-check this is actually the case?
----------------------------------------------------------
Karl Kliparchuk, M.Sc.
McElhanney Consulting Services Ltd.
L100 - 780 Beatty Street
Vancouver, BC Canada
V6B 2M1
Tel (604) 683-8521
Email: [EMAIL PROTECTED]
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