I was thinking ST_Difference might work, but unfortunately that would return the red regions thought it would leave out the green.
Hope that helps, Regina -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of diplonics Sent: Thursday, May 14, 2009 2:10 PM To: [email protected] Subject: [postgis-users] Viewshed Isovist Hi All, Just wondering if this can be done in PostGIS and if not does anyone know of the simplest method to get it done. I have 2 PostGIS polygon geometry tables and I want to basically do is an isovist/viewshed/line of sigth operation. I know an intersection operation can isolate where the polys are spatially equal but what I want is some sort of set complement operation where it will also remove all polygon sections without direct line of sight. Image 1 is a sample of my two data sets. The purple polys are building outlines while the yellow poly is an unobstructed viewshed from a line. http://www.nabble.com/file/p23546020/ViewShed01.png Image 2 is a sample of the desired result. Using a PostGIS intersection operation I can isolate the green sections, but I want to return a geometry that is the yellow section with the green and red sections removed. http://www.nabble.com/file/p23546020/ViewShed02.png Any advice on this problem, or links to help, would be greatly appreciated. Thanks -- View this message in context: http://www.nabble.com/Viewshed-Isovist-tp23546020p23546020.html Sent from the PostGIS - User mailing list archive at Nabble.com. _______________________________________________ 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
