I think for this case, this behavior is expected.
When you say – it used to return ‘POINT Z(0 0 2.5)’ which version of GEOS and
PostGIS were you running?
If you passed in a 2 dimensional point and a 3-dimentional line, then you would
get interpolation on the z as it would treat the 2-D point as an infinite
vertical line.
Take for example:
SELECT ST_AsText(ST_intersection('POINT(0 0)'::geometry, 'LINESTRINGZ ( 0 0 5,
0 0 3, 0 2 3)'::geometry));
Yields: POINT Z (0 0 4)
But in the case of a point 3d and a point 3d line. The routine I think it goes
thru is
1) 2D intersects – yes they intersect
2) If one is a 3d point, then return the point
If you gave it two 3D linestrings or a polygon, you should see the
interpolation behavior you are expecting.
From: postgis-users [mailto:[email protected]] On Behalf Of
Alexandre Neto
Sent: Thursday, April 27, 2023 11:28 AM
To: PostGIS Users Discussion <[email protected]>
Subject: [postgis-users] st_intersection of 3D objects
Hi,
PostGIS documentation for the st_intersection
<https://postgis.net/docs/ST_Intersection.html> states the following
If working with 3D geometries, you may want to use SFGCAL based
ST_3DIntersection <https://postgis.net/docs/ST_3DIntersection.html> which does
a proper 3D intersection for 3D geometries. Although this function works with
Z-coordinate, it does an averaging of Z-Coordinate.
I have used that averaging in the past, but it seems that I can no longer use
it in PostgreSQL 14 and PostGIS 3.3.2 (POSTGIS="3.3.2 4975da8" [EXTENSION]
PGSQL="140" GEOS="3.10.2-CAPI-1.16.0" PROJ="8.2.1" LIBXML="2.9.13"
LIBJSON="0.15" LIBPROTOBUF="1.3.3" WAGYU="0.5.0 (Internal)")
SELECT ST_AsText(ST_Intersection('POINTZ(0 0 0)'::geometry, 'LINESTRINGZ ( 0 0
5, 0 2 5)'::geometry));
Used to return:
'POINT Z (0 0 2.5)'
but now it returns
'POINT Z (0 0 0)'
Is this expected or a bug.
Greetings,
Alexandre Neto
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