Tony, Just to add to what everyone else has said. Be careful with long lat data. Buffering in long lat does not produce a circle since the distance would be in degree units and be applied using planar geometry. You'll want to transform to planar like some UTM space.
Here is a response I gave to someone that asked me a similar question. http://www.bostongis.com/blog/index.php?/archives/28-Using-generate_series-t o-Generate-Test-Spatial-Data.html#c419 though new function page is (utmzone function is on this page that is referred to above) http://trac.osgeo.org/postgis/wiki/UsersWikiplpgsqlfunctions (I guess we should break out all those functions) Anyrate if all your data can fit in a UTM or some state plane you would be advised to transform to that spatial ref before doing these calculations. then you could just use ST_Dwithin. You don't necessarily need to store your data in a planar projection, but you should have a functional index on that projection. For US data I like to use 2163 (for somewhat decent measurement -- its not as good as state plane or utm but provides good enough measurement for my wide ranging distance US calcs and covers all of continental US). Hope that helps, Regina -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Tony Elmore Sent: Tuesday, April 14, 2009 1:27 AM To: [email protected] Subject: [postgis-users] Finding points in a circle Admittedly, I have not spent a tremendous amount of time with this yet - so I'm not really asking for a solution here, but would like some feedback to determine if I'm on the right track. Is this scenario possible using postGIS? i have many items (hundreds of thousands) with each item containing a lat / lng and a radius (each item could have a different radius). The circle created by the lat / lng and radius for each item would in all likelihood overlap with other items. Given a random point, is it possible to retrieve all of the rows where the random point is inside the circle created from the lat / lng and radius? I would assume I should create the circle for each item first and store that as geometry. Could someone please verify that this scenario is appropriate for postgis. Regards, Tony _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
