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justdream
2009-05-02, 04:24 AM
how to know the Datum of any country?
Thanks

byja
2009-05-02, 04:52 AM
Why bother? Use polar coordinates in WGS84 datum.

proy1_10
2009-05-02, 05:47 AM
Earth isn't a perfect sphere nor an ellipsoid. Usually countries choose one model as accurated as possible to real earth (only valid in a region)
A datum is An ellipsoid+point where earth & ellipsoid are tangents.
Europe usually uses ED50
U.S.A. NAD83...
WGS84 is universal system so as say byja you can convert all coordinates to WGS84 and work only with this datum
Every system had some little corrections...

venom
2009-05-02, 06:23 AM
how to know the Datum of any country?
Thanks

Dear bruv,

there are so many posts already about mapdata here. Obviously, before downloading Height/elevation, clutter data for your country, you should know about the term "Datum". The best and easiest definition which i ever found is:

A datum is a set of constants, specifying the coronate system used for geodetic referencing, i.e., for calculating coordinates of points on the Earth. ( Ref. the NGS (National Geodetic Survey).

Specific geodetic datums are usually given distinctive names. In other words, a datum is a set of parameters and reference points used to mathematically define the three-dimensional shape of the Earth (e.g., as a spheroid).

For example, the "North American Datum for 1983" (NAD83) is the datum for map projections and coordinates within the United States and throughout North America.

It means we can represent our 3D Earth in different ways, therefore having many Datums. One of the most popular Datum is UTM (Universe Transverse Mercator) . I will not go in much detail of it but you can read about it at the following Link.


http://www.uwgb.edu/dutchs/FieldMethods/UTMSystem.htm


Now coming back to your question of how to know about your country datum. I can tell you the way of looking at the UTM Datum of your country. Now UTM again has several vesions, like WGS72, WGS79, WGS84 etc, WGS84 is the latest one which everyone usually follows. Please visit the following Link, if you know the Longitude of your location then you can find our the ZONE easily.


http://www.apsalin.com/utm-zone-finder.aspx

OR


Formula to find out the zone is : ZoneNumber = Roundup (( Longitude - 180) / 6)


If you are following WGS84 then you should know the ZONE Number with the North or South Information. If your country lies above the equator then it is Northern Zone, if below Equator then Southern Zone. See the Image attached or if you need the better resolution then download the projection image in rar file. I hope it helps, cheers