Hello!!<br>Take a look at this email, from the PostGIS mailing list:<br><a href="http://www.nabble.com/function-to-find-UTM-zone-SRID-from-POINT-tf669268.html#a1772300">http://www.nabble.com/function-to-find-UTM-zone-SRID-from-POINT-tf669268.html#a1772300
</a><br><br>Hope this help<br>Leandro<br><br><br><br><div><span class="gmail_quote">2007/10/26, Barend Köbben <<a href="mailto:kobben@itc.nl">kobben@itc.nl</a>>:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Hi Linda,<br><br>I think your question starts with a basic mis-assumption:<br><br>> Basically if I pass in the x,y coordinates in WGS_84 or any other meter<br>> projection<br><br>WGS84 is a officially a Datum, not a projection. A Datum is a global or
<br>ellipsoidal object closely matching the Earth's shape. A projection is<br>literaly what it says: a projection of that global object on a flat surface.<br><br>(for a good overview, I suggest <a href="http://kartoweb.itc.nl/geometrics/">
http://kartoweb.itc.nl/geometrics/</a>)<br><br>What most people mean if they say "WGS84 projection" is "Geographic<br>coordinates (in latitude, longitude) on the WGS_84 Datum". Therefore it's<br>coordinates are NOT x,y but lat,lon and it's NOT a meter projection but a
<br>(decimal) degrees description of a vector to a point on the surface of a<br>global object (actually the lat and lon are angles with respect to the<br>globe's origin...).<br>In more simpel terms: lat,lon does not have a cartesian grid with an origin
<br>and equal values along two axes as its mathematical basis, as the UTM and<br>other (meter) projections have.<br><br>> I would like it to return the zone that those coordinates are in.<br>You can easily do that if indeed you have lat,lon coordinates as described
<br>above. As the zones of UTM are just 60 zones divided over the 360 degrees of<br>longitude, each zone is 360/60=6 degrees of longitude. Zone 1 is from -180<br>to 174, zone 31 is from 0 (Greenwich) to 6, etcetera. The zones each have a
<br>N-S divide over the equator, so if the latitude is positive, the zone is<br>zone xN, if negative it's zone xS.<br>So my city Enschede is at lat,lon= 52.2166667 , 6.9 and therefore in zone<br>31N.<br><br>For "any other meter projection" it's not so easy, because the projections
<br>all use different origins of their grid. The best is to calculate the<br>projected x,y back to lat,lon on the WGS84 (in PROJ4-based systems use the<br>toWGS84 part of the projection description) and then to the UTM zone...
<br><br>Yours,<br>__<br>Barend Köbben<br>International Institute for Geo-information<br>Sciences and Earth Observation (ITC)<br>PO Box 6, 7500AA Enschede (The Netherlands)<br>ph: +31 (0)53 4874253; fax: +31 (0)53 4874335<br>
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