[postgis-tickets] [PostGIS] #4897: Interiors of st_difference(geom_a, geom_b) and geom_b intesects

[PostGIS]

#4897: Interiors of st_difference(geom_a, geom_b) and geom_b intesects
---------------------+---------------------------
 Reporter:  fiedt    |      Owner:  pramsey
     Type:  defect   |     Status:  new
 Priority:  medium   |  Milestone:  PostGIS 3.1.2
Component:  postgis  |    Version:  3.0.x
 Keywords:           |
---------------------+---------------------------
 Hi,

 i have an unexpected result of st_difference as it intersects the second
 input geometry according to st_relate.

 {{{
 WITH my_geoms AS (
     -- first geometry
         SELECT 1 AS id, st_geomfromtext('MULTIPOLYGON(((596365.1172897
 5963971.50783237,596356.365586281 5963985.76622559,596393.339074884
 5963985.76622559,596388.520721316 5963963.93613391,596365.1172897
 5963971.50783237)))') AS geom
         UNION
         -- second geometry
         SELECT 2 AS id, st_geomfromtext('MULTIPOLYGON(((596368.067302089
 5963988.71623797,596368.657304566 5963965.21447261,596337.190505754
 5963970.32782742,596337.878841978 5963989.30624045,596368.067302089
 5963988.71623797)))') AS geom),
         diff_geom AS (
         -- geometry in the exterior of second geometry
         SELECT 3 AS id, st_difference(t1.geom, t2.geom) AS geom FROM
 my_geoms t1, my_geoms t2 WHERE t1.id = 1 AND t2.id = 2)
 -- i expect only the first geometry 'relates' here (interiors intersect)
 ...
 SELECT * FROM my_geoms, diff_geom WHERE st_relate(diff_geom.geom,
 my_geoms.geom, '2********');
 -- ... but two rows returned
 }}}

 The result is as expected, if ...
 - i use st_snaptogrid(...) even with a tiny gridsize like 0.00000001
 - round coordinates to integers

 My config:

 {{{
 SELECT postgis_full_version();
 }}}

 POSTGIS="3.0.3 3.0.3" [EXTENSION] PGSQL="130" GEOS="3.8.1-CAPI-1.13.3"
 PROJ="7.1.1" LIBXML="2.9.9" LIBJSON="0.12" LIBPROTOBUF="1.2.1"
 WAGYU="0.4.3 (Internal)"

 Thanks in advance.

-- 
Ticket URL: <https://trac.osgeo.org/postgis/ticket/4897>
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