Name
ST_CoverageInvalidEdges — Window function that finds locations where polygons fail to form a valid coverage.
Synopsis
geometry ST_CoverageInvalidEdges(geometry winset
geom, float8
tolerance = 0);
Description
A window function which checks if the polygons in the window partition form a valid polygonal coverage. It returns linear indicators showing the location of invalid edges (if any) in each polygon.
A set of valid polygons is a valid coverage if the following conditions hold:
Non-overlapping - polygons do not overlap (their interiors do not intersect)
Edge-Matched - vertices along shared edges are identical
As a window function a value is returned for every input polygon. For polygons which violate one or more of the validity conditions the return value is a MULTILINESTRING containing the problematic edges. Coverage-valid polygons return the value NULL. Non-polygonal or empty geometries also produce NULL values.
The conditions allow a valid coverage to contain holes (gaps between polygons),
as long as the surrounding polygons are edge-matched.
However, very narrow gaps are often undesirable.
If the tolerance parameter is specified with a non-zero distance,
edges forming narrower gaps will also be returned as invalid.
The polygons being checked for coverage validity must also be valid geometries. This can be checked with ST_IsValid.
Availability: 3.4.0
Requires GEOS >= 3.12.0
Examples
Invalid edges caused by overlap and non-matching vertices
WITH coverage(id, geom) AS (VALUES
(1, 'POLYGON ((10 190, 30 160, 40 110, 100 70, 120 10, 10 10, 10 190))'::geometry),
(2, 'POLYGON ((100 190, 10 190, 30 160, 40 110, 50 80, 74 110.5, 100 130, 140 120, 140 160, 100 190))'::geometry),
(3, 'POLYGON ((140 190, 190 190, 190 80, 140 80, 140 190))'::geometry),
(4, 'POLYGON ((180 40, 120 10, 100 70, 140 80, 190 80, 180 40))'::geometry)
)
SELECT id, ST_AsText(ST_CoverageInvalidEdges(geom) OVER ())
FROM coverage;
id | st_astext
----+---------------------------------------
1 | LINESTRING (40 110, 100 70)
2 | MULTILINESTRING ((100 130, 140 120, 140 160, 100 190), (40 110, 50 80, 74 110.5))
3 | LINESTRING (140 80, 140 190)
3 | null
-- Test entire table for coverage validity
SELECT true = ALL (
SELECT ST_CoverageInvalidEdges(geom) OVER () IS NULL
FROM coverage
);