If your data are globally distributed (as you said they are), then UTM probably isn't the best choice. A global equal-area projection would be better, in that you can use the same parameters regardless of where on the globe you're working. I have a similar application, and use Cylindrical Equal Area. I use something like (with an old version of PostGIS -- I think the function names all start with ST_ now):
select sum(area(transform(glacier_polys,32767))) FROM glacier_polygons ... Note that the EPSG code here is one I defined. I think the current version of PostGIS might have CEA projection defined in some proper location. Bruce On Mon, Sep 8, 2008 at 7:36 PM, Robert Coup <[EMAIL PROTECTED]> wrote: > On Tue, Sep 9, 2008 at 3:14 AM, Nicolas Ribot <[EMAIL PROTECTED]> wrote: >> >> No for surfaces. You will have to project your data into a planar >> projection system to do so (UTM for instance). This thread may be >> useful in your case to find the correct UTM zone according to your >> objects coordinates: > > Untrue, the maths is just a little harder! And you need to assume the globe > is a sphere (ala distance_sphere()): > If you're dealing with lat-lon "rectangles" you want something like this: > http://mathforum.org/dr.math/faq/formulas/faq.sphere.html#spherecap > If you're dealing with arbitrary polygons its a bit more complicated: > http://groups.google.com/group/comp.infosystems.gis/browse_frm/thread/af0401d07c3068b5?lnk=igtc > HTH, > Rob :) > _______________________________________________ > postgis-users mailing list > [email protected] > http://postgis.refractions.net/mailman/listinfo/postgis-users > > -- Bruce Raup http://cires.colorado.edu/~braup/ _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
