Roman, I think you will want to stay away from ellipsoid for now or at least until PostGIS 2.0 (or 1.5 comes out). Those in current PostGIS just deal with point geometries and not terribly well. I think your best bet is to find a spatial ref that covers all of Nigeria. It won't be quite as accurate but will save you having to worry about dealing with 2 or 3 sets of spatial refs. These links might help http://lists.maptools.org/pipermail/proj/2008-December/004145.html http://www.spatialreference.org/ref/?search=africa You could formulate your own from proj constructs that is more accurate than above (and covers the 2 srids you mentioned), but that's not my strength Leo
_____ From: [email protected] [mailto:[email protected]] On Behalf Of Smith Roman Sent: Thursday, August 06, 2009 3:21 AM To: Users Postgis Subject: Re: [postgis-users] countries with more than one srid ? Hi everyone, Since I intend placing all my states data in one table, are u suggesting that I leave my data in wgs 84 (lon & lat) then do my distance calculations on the WGS 84 ellipsoid ? How can this be done in postgis ? The distance calculations I need to do in my application are nearest neighbour and where are my queries. A sample query for doing distance calculations on the ellipsoid in postgis will be helpful. Cheers, Roman
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