There's a difference between astronomical latitude and longitude and geodetic
latitude and longitude. Prof. Charles Merry at the University of Cape Town
should be able to help you out with the specifics of geodetic datums used in
South Africa: [EMAIL PROTECTED]
-- Richard Langley
Professor of Geodesy and Precision Navigation
On Wed, 13 Jan 1999, Anton Reynecke wrote:
>Apologies for this non-sundial question, but I do hope someone can help.
>
>I've always been under the impression that Latitude/Longitude is a universal
>and unambigious method of indicating a position on the earth but now I am
>not so sure....
>
>In South-Africa, the National survey system is based on a Gauss conform
>system with the Clarke 1880 (Modified) Ellipsoid.
>
>It is fundamentaly the same as the wordwide UTM system, with a slightly
>different scale factor, and the width of a system is only two degrees in
>longitude, one on either side of a central meridian, whereas UTM covers six
>degrees.
>
>Now the National system is based on the the same projection but we are using
>the WGS 84 ellipsoid.
>
>That caused the Latitude of a fixed point to increase South by 2,04 arc
>seconds, and Longitude West by 1,06 arc seconds (approximately), and the
>projected co-ordinates changed by approx. 296 metres South and 27 metres
>West (Differences calculated by comparing coordinates from the old system
>with the new system, around Pretoria).
>
>I am under the impession that Lat/Long is astronomically fixed from distant
>objects, with the origin being the rotation axis of the earth, so how can
>the values be influenced by adopting a new ellipsoid ?
>
>What fundamentals am I missing?
>
>
>D. Anton Reynecke
>
>
>
>
>
>
>
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Richard B. Langley E-mail: [EMAIL PROTECTED]
Geodetic Research Laboratory Web: http://www.unb.ca/GGE/
Dept. of Geodesy and Geomatics Engineering Phone: +1 506 453-5142
University of New Brunswick Fax: +1 506 453-4943
Fredericton, N.B., Canada E3B 5A3
Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/
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