On Feb 10, 2022, at 4:55 PM, Emily Gouge <ego...@refractions.net> wrote:
I have a linear dataset on which I was building a query to find edges that are
“very close” but don’t touch. While working on this query I found some
unexpected results with the st_intersects and st_disjoint functions. As
outlined below, the query returned true for both st_instersects and st_disjoint
for a few geometries comparisons, but ONLY when a where clause was used to
filter the geometries spatially. When unique identifiers were used to filter
geometries only st_disjoint returns true.
Versions:
Except where noted otherwise the results below reference testing on these
versions:
POSTGIS="3.2.0 3.2.0" [EXTENSION] PGSQL="140" GEOS="3.10.1-CAPI-1.16.0" PROJ="7.2.1" LIBXML="2.9.9"
LIBJSON="0.12" LIBPROTOBUF="1.2.1" WAGYU="0.5.0 (Internal)"
PostgreSQL 14.1, compiled by Visual C++ build 1914, 64-bit
When I run this query:
select a.id, b.id,
st_intersects(a.geometry, b.geometry),
st_intersects(b.geometry, a.geometry),
st_disjoint(a.geometry, b.geometry),
st_disjoint(b.geometry, a.geometry)
from test.eflowpath a, test.eflowpath b
where a.id != b.id
and st_dwithin(a.geometry, b.geometry, 0.00001)
and st_disjoint(a.geometry, b.geometry);
PostGIS 3.2: 50 rows were returned, but there are three rows that return true
for both st_disjoint and st_intersects. Given the query this in itself is a bit
odd as you'd expect reciprocal results for the pairs of the geometry (so at
least 4 rows).
-------
889105be-5782-43f1-b50c-5a5825c83875
e5703673-a995-472e-b4b4-0280143eba0c
true
true
true
true
-------
0d05aabb-9ff3-4d8f-b6c7-b2b44b0868c8
3a09b2af-5932-4e36-9e3e-d8109e5463fa
true
true
true
true
-------
3a09b2af-5932-4e36-9e3e-d8109e5463fa
0d05aabb-9ff3-4d8f-b6c7-b2b44b0868c8
true
true
true
true
-------
...
Note: In PostGIS 3.1.2 50 rows were returned by only two rows returned true for
both disjoint and intersects.
HOWEVER,
When I compare one pair of those edges specifically using the ids they are only
disjoint (which is the result I would expect to see)
select a.id, b.id,
st_intersects(a.geometry, b.geometry),
st_intersects(b.geometry, a.geometry),
st_disjoint(a.geometry, b.geometry),
st_disjoint(b.geometry, a.geometry)
from test.eflowpath a, test.eflowpath b
where b.id = '889105be-5782-43f1-b50c-5a5825c83875' and a.id =
'e5703673-a995-472e-b4b4-0280143eba0c'
Results:
-------
e5703673-a995-472e-b4b4-0280143eba0c
889105be-5782-43f1-b50c-5a5825c83875
false
false
true
true
-------
I thought perhaps this had something to do with the indexes so I removed all
geometry indexes from the table and re-ran the initial query. In postgis 3.2
this returned the same results as the indexed query.
Note: In PostGIS 3.1.2 this also returned three rows with intersects and
disjoint true. As noted above with indexes in 3.1.2 only 2 rows were returned
where intersects and disjoint were true.
Similar results occurred if st_dwithin from the where statement was increased
to 0.01.
Test Data: When I made a table with only the edges in question all queries
returned expected results: st_intersects is false and st_disjoint is true. As a
result providing a small test case for this issue doesn’t seem possible. But I
am happy to provide all the data - there are 27,444 rows.
While this isn’t a problem for me, I find it unexpected that the results from
st_intersects and st_disjoint of two geometries would be different based on the
where clause in the query (and the data in the table).
Thoughts?
