Intersection between mixed dimensions

[michaudm]

Intersection between 3D and 2D geometries is generally smart (interpolate z on the 3D geometry). But in the case where the intersection point matches exactly a vertex of one of the geometries, it returns this vertex, either a 2D Point or a 3D Point. As a result, an intersection layer build from the intersection of a 2D layer and a 3D layer may be a mix of 2D and 3D points. But the worst case arises if two geometries have multiple intersections, some matching a 2D vertex and others a 3D one. Here, the process stops with error :

ERROR:  lwcollection_construct: mixed dimension geometries: 0/2 

You can reproduce with the following simple test case :

select ST_Z(ST_Intersection(
	ST_GeomFromText('LINESTRING(0 0, 5 5, 10 10, 20 0)'),
	ST_GeomFromText('LINESTRINGZ(0 10 100, 10 0 100, 15 5 100, 20 10 100)')
))

[robe]

I confirmed this is still an issue in PostGIS 2.5.2 and yet to be released 3.0.0alpha4

[pramsey]

I don't see this result against GEOS 3.8

select st_asewkt(ST_Intersection(
  ST_GeomFromText('LINESTRING(0 0, 5 5, 10 10, 20 0)'),
  ST_GeomFromText('LINESTRINGZ(0 10 100, 10 0 100, 15 5 100, 20 10 100)')
));

          st_asewkt           
------------------------------
 MULTIPOINT(5 5 100,15 5 100)