Hi Denis, Thank you for your reply.
Actually I really want to test a LINESTRING against POLYGON centroids (determined with ST_PointOnSurface), not just a line against a point. Is this question not answerable? As a human I can determine it. I am aware about the edge cases where a point is on the line, but in my case this can't happen as the data comes from a correctly defined polygon mosaic. >From the lines of a polygon mosaic (directed lines node to node, no double lines) I want to label what is left and what is right of a polygon border. My theme is usage zones and I should label what is left and right of the polygon border. Andreas Am 23.07.2013 16:48, schrieb Denis Rouzaud: > Oops, here is the complete code: > > pointGeom << ST_Intersection( ST_MakeLine( > ST_MakePoint(ST_XMin(lineGeom), ST_Y(pointGeom)), > ST_MakePoint(ST_XMax(lineGeom), ST_Y(pointGeom)) > ), lineGeom > ) > > > > On 07/23/2013 04:31 PM, Denis Rouzaud wrote: >> Hi Andreas, >> >> Do you mean you want to test to a segment? >> >> Because, I can't see a true answer for a line. >> >> If you want to do test to a segment, it should do the job to test if >> the intersection with the horizontal line (dy=0) over your point and >> your input line is on the left/right to your point. >> >> So, maybe test: >> >> pointGeom << ST_Intersection( ST_MakeLine( >> ST_MakePoint(ST_XMin(lineGeom), ST_Y(pointGeom)), >> ST_MakePoint(ST_XMax(lineGeom), ST_Y(pointGeom)) >> ) >> >> You have to handle the case where your segment is horizontal, but then >> a simple test with ST_Xmin/max should be enough. >> >> Cheers, >> >> Denis >> >> On 07/23/2013 03:54 PM, Andreas Neumann wrote: >>> 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
