ST_CoverageSimplify — Window function that simplifies the edges of a polygonal coverage.
geometry ST_CoverageSimplify(
geometry winset
geom, float8
tolerance, boolean
simplifyBoundary = true)
;
A window function which simplifies the edges of polygons in a polygonal coverage. The simplification preserves the coverage topology. This means the simplified output polygons are consisent along shared edges, and still form a valid coverage.
The simplification uses a variant of the Visvalingam–Whyatt algorithm.
The tolerance
parameter has units of distance,
and is roughly equal to the square root of triangular areas to be simplified.
To simplify only the "internal" edges of the coverage (those that are shared by two polygons) set the simplifyBoundary
parameter to false.
If the input is not a valid coverage there may be unexpected artifacts in the output (such as boundary intersections, or separated boundaries which appeared to be shared). Use ST_CoverageInvalidEdges to determine if a coverage is valid. 
Availability: 3.4.0
Requires GEOS >= 3.12.0


WITH coverage(id, geom) AS (VALUES (1, 'POLYGON ((160 150, 110 130, 90 100, 90 70, 60 60, 50 10, 30 30, 40 50, 25 40, 10 60, 30 100, 30 120, 20 170, 60 180, 90 190, 130 180, 130 160, 160 150), (40 160, 50 140, 66 125, 60 100, 80 140, 90 170, 60 160, 40 160))'::geometry), (2, 'POLYGON ((40 160, 60 160, 90 170, 80 140, 60 100, 66 125, 50 140, 40 160))'::geometry), (3, 'POLYGON ((110 130, 160 50, 140 50, 120 33, 90 30, 50 10, 60 60, 90 70, 90 100, 110 130))'::geometry), (4, 'POLYGON ((160 150, 150 120, 160 90, 160 50, 110 130, 160 150))'::geometry) ) SELECT id, ST_AsText(ST_CoverageSimplify(geom, 30) OVER ()) FROM coverage; id  st_astext + 1  POLYGON ((160 150, 110 130, 50 10, 10 60, 20 170, 90 190, 160 150), (40 160, 66 125, 90 170, 40 160)) 2  POLYGON ((40 160, 66 125, 90 170, 40 160)) 3  POLYGON ((110 130, 160 50, 50 10, 110 130)) 3  POLYGON ((160 150, 160 50, 110 130, 160 150))