Opened 5 months ago
Closed 3 months ago
#5740 closed defect (fixed)
ST_DistanceSpheroid doesn't return 0 when one geometry contains the other
Reported by: | cdestigter | Owned by: | pramsey |
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Priority: | medium | Milestone: | PostGIS 3.4.3 |
Component: | postgis | Version: | 3.4.x |
Keywords: | Cc: |
Description (last modified by )
The docs say
Returns minimum distance in meters between two lon/lat geometries given a particular spheroid
Based on this description it seems that any intersection between the two geometries should cause the result to be 0 (the minimum distance between the geometries is 0 because they overlap)
However, it seems that actually compares the _edges_ of the geometries - if one geometry contains the other you get a positive number:
-- touching the edge of the polygon, the result is zero => select st_distancespheroid('SRID=4326;POLYGON((0 0,0 1,1 1,1 0,0 0))'::GEOMETRY, 'SRID=4326;POINT(0 0.5)'::geometry); 0 -- close to the edge, the result is nonzero => select st_distancespheroid('SRID=4326;POLYGON((0 0,0 1,1 1,1 0,0 0))'::GEOMETRY, 'SRID=4326;POINT(0.1 0.5)'::geometry); 11131.528045775543 -- the further you get from the edge, the larger the result => select st_distancespheroid('SRID=4326;POLYGON((0 0,0 1,1 1,1 0,0 0))'::GEOMETRY, 'SRID=4326;POINT(0.5 0.5)'::geometry); 55657.640177233385
Interestingly, ST_DistanceSphere
gives the expected result:
=> select st_distancesphere('SRID=4326;POLYGON((0 0,0 1,1 1,1 0,0 0))'::GEOMETRY, 'SRID=4326;POINT(0.5 0.5)'::geometry); 0
Change History (8)
comment:1 by , 5 months ago
Description: | modified (diff) |
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comment:3 by , 3 months ago
Hm, I really thought we had all these things draining into the geography code path by now.
comment:5 by , 3 months ago
Yep, a little more subtle. The geometry bounding box was sneaking into the geodetic covers operation, causing a mis-fire when the code started from a geometry (as in this example).
comment:8 by , 3 months ago
Resolution: | → fixed |
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Status: | new → closed |
I've had a browse around the code, and it seems like the bug is here - the code checks for edge intersections and returns 0 if there are any but it doesn't check for containment.
I'm not sure how ST_DistanceSphere avoids the issue since it looks like it probably goes down a similar codepathST_DistanceSphere actually has the same issue IF you explicitly provide the optional third parameter (world radius in metres)
It looks like if you omit that parameter it doesn't use the buggy codepath - instead it casts your geometries to geographies and calls
geography_distance
which doesn't have the same problem.