I use this. Works but its quite a few years old, maybe another way now.
If line goes from A to B and point is P, v = (Ay-By)*Px+(Bx-Ax)*Py+(Ax*By-Bx*Ay) v>0: "Left" v<0: "Right" v=0: "On the line" (or in front of B / behind A) select sites_gid, roads_gid, case when ( st_y(st_startpoint(sline)) - st_y(st_endpoint(sline)) ) * st_x(cpoint) + ( st_x(st_endpoint(sline)) - st_x(st_startpoint(sline)) ) * st_y(cpoint) + ( st_x(st_startpoint(sline)) * st_y(st_endpoint(sline)) - st_x(st_endpoint(sline)) * st_y(st_startpoint(sline)) ) > 0 then 'L' when ( st_y(st_startpoint(sline)) - st_y(st_endpoint(sline)) ) * st_x(cpoint) + ( st_x(st_endpoint(sline)) - st_x(st_startpoint(sline)) ) * st_y(cpoint) + ( st_x(st_startpoint(sline)) * st_y(st_endpoint(sline)) - st_x(st_endpoint(sline)) * st_y(st_startpoint(sline)) ) < 0 then 'R' when ( st_y(st_startpoint(sline)) - st_y(st_endpoint(sline)) ) * st_x(cpoint) + ( st_x(st_endpoint(sline)) - st_x(st_startpoint(sline)) ) * st_y(cpoint) + ( st_x(st_startpoint(sline)) * st_y(st_endpoint(sline)) - st_x(st_endpoint(sline)) * st_y(st_startpoint(sline)) ) = 0 then null end as side from ... Eric Randall, GIS DB Admin/Analyst County of Erie, Pa 140 West 6th Street Room 111 Erie, Pa 16501 Ph. 814-451-6063 Fx. 814-451-7000 L'unica via d'uscita รจ dentro --Alice -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Andreas Neumann Sent: Tuesday, July 23, 2013 9:54 AM To: [email protected] Subject: [postgis-users] Left of/Right of test Hi, I want to test a point if it is left-of or right-of a given LINESTRING. I found the << >> and &< &> but they do not behave like I expected. Perhaps it is because they only test on the bounding box level and not on the real geometry? Is there a left/right of test available on the geometry instead of the bounding box? Thank you, Andreas _______________________________________________ postgis-users mailing list [email protected] http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users _______________________________________________ postgis-users mailing list [email protected] http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
