PostGIS 1.5.8 Manual - Fedora Project Packages GIT repositories

PostGIS 1.5.8 Manual30 / 310For example, consider a linear dataset representing a road network. It may be the task of a GIS analyst to identify all roadsegments that cross each other, not at a point, but on a line, perhaps invalidating some business rule. In this case,ST_Crosses does not adequately provide the necessary spatial filter since, for linear features, it returns true only wherethey cross at a point.One two-step solution might be to first perform the actual intersection (ST_Intersection) of pairs of road segments thatspatially intersect (ST_Intersects), and then compare the intersection’s ST_GeometryType with ’LINESTRING’ (properlydealing with cases that return GEOMETRYCOLLECTIONs of [MULTI]POINTs, [MULTI]LINESTRINGs, etc.).A more elegant / faster solution may indeed be desirable.