[postgis-users] st_intersects and st_disjoint inconsistent results

Fri Feb 11 14:49:27 PST 2022

It seems to be predicate robustness failure week!  The geometries in this
recent post show the same problem (in JTS, and probably GEOS too).

https://lists.osgeo.org/pipermail/postgis-users/2022-February/045255.html

A: LINESTRING (-29796.696826656284 138522.76848210802, -29804.3911369969
138519.3504205817)
B: LINESTRING (-29802.795222153436 138520.05937757515, -29802.23305474065
138518.7938969792)

A.disjoint(B) = TRUE
A.preparedIntersects(B) = TRUE

(Note: the post issue is slightly different - it just happens that the data
shows this problem)

On Fri, Feb 11, 2022 at 2:19 PM Paul Ramsey <pramsey at cleverelephant.ca>
wrote:

> This issue has been confirmed on both GEOS and JTS. You have magic
> geometry that breaks the consistency between prepared and standard results.
>
> https://github.com/libgeos/geos/pull/566
>
> P.
>
> > On Feb 10, 2022, at 6:43 PM, Emily Gouge <egouge at refractions.net> wrote:
> >
> > Here you go.  Thanks!
> >
> >
> > SELECT ST_AsHEXEWKB (geometry) FROM test.eflowpath WHERE id =
> '889105be-5782-43f1-b50c-5a5825c83875'
> >
> >
> 01020000200912000007000000642F25DC75A24CC0E4DE5740FCB34840A7CEFE9B72A24CC09DA85B2CFBB34840B5519D0E64A24CC091FAA188FBB34840FA449E245DA24CC054C2137AFDB34840F4ACFFCE51A24CC09FEB562A03B448405328C1D144A24CC09A3DD00A0CB44840404C10C03CA24CC0EA07FE6910B44840
> >
> > SELECT ST_AsHEXEWKB (geometry) FROM test.eflowpath WHERE id =
> 'e5703673-a995-472e-b4b4-0280143eba0c'
> >
> >
> 0102000020091200000E00000004BE47A23CA24CC098A1F14410B448409871AEBC3FA24CC078341F2114B448400858AB764DA24CC09D0546031DB448406BFD3E2D50A24CC0BEDDEDD522B4484004824AA654A24CC02DC9A60128B44840EE377FB850A24CC0FA18BD642DB44840CCAF8B474EA24CC02CCCE78134B44840D7158E7B4EA24CC01D7C17A53AB44840ACFA01B452A24CC02688BA0F40B44840DB508C8752A24CC006CDF80846B44840A1F31ABB44A24CC0C891730756B44840009AF7EE45A24CC06B7649415CB448408C2ECAC749A24CC0CE57248161B44840A74302A150A24CC07DD00E1368B44840
> >
> > On 2022-02-10 5:57 p.m., Paul Ramsey wrote:
> >>> On Feb 10, 2022, at 4:55 PM, Emily Gouge <egouge at 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?
> >> The fact that a single test case returns one result, but results in a
> larger set returns another says to me that likely the issue in different
> code lines because of different cache behaviour. When you do the single
> test case you get a brute force intersects. When you do several in a batch,
> you get prepared geometry (at least, for the cases that happen after
> caching).
> >> If you can provide the HEXWKB of the two geometries that showed
> disagreement (where b.id = '889105be-5782-43f1-b50c-5a5825c83875' and a.id
> = 'e5703673-a995-472e-b4b4-0280143eba0c') we can set up a test case in GEOS
> that compares the normal and prepared geometry calls and see if that's the
> problem.
> >> P.
> >>>
> >>> Thanks,
> >>> Emily
> >>> _______________________________________________
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