Hi, Given streets linestrings and forest polygons, think of all streets segments which are *not* inside forest areas. How can I calculate all segments from linestrings which do not intersect polygons?
Any ideas? - S. Attempt 1: ST_SymDifference sounds good! But even this equivalent produces nonsense: # SELECT ST_AsText( ST_CollectionExtract(ST_Difference(ST_Union(ls.way,po.way), ST_Intersection(ls.way,po.way)),2) ) FROM linestring ls, polygon po Attempt 2: # SELECT ST_AsText(ST_Intersection(ls.way, po.way)) FROM linestring ls, polygon po gives me all streets *inside* forests. But I'd like get the "remainder" in between... Attempt 3: # SELECT ST_AsText(ST_Difference(ls.way, po.way)) FROM linestring ls, polygon po gives me two displaced lines for each street (because the resultse contains the difference between one line and one polygon), Thesse two could be intersected - but ST_Intersection of two overlapping lines (with same nodes except end nodes) does'nt seem to work. Attempt 4: In a very desperate idea, I calculcated the extent of both tables in order generate a huge boundary polygon with has as many wholes as there are polygons. Then I could do an ST_Intersect of this big swiss cheese polygon with the lines - but no luck. Attempt 5: I finally tried to dump all points from Attempt 2 (intersection) to get hold of the boarder points where lines and polygons cross. But when tried to split a line at a point and to sort out all lines outside polygons things got again complicated.. _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
