Description

Simplifies a geometry using SFCGAL's simplification algorithm, which reduces the number of points or vertices while preserving the essential features of the geometry. This function preserves Z and M values during simplification.

The algorithm is based on constrained triangulation and uses the CGAL Polyline Simplification 2 library with additional handling to preserve Z and M coordinates. When topology is preserved and geometries intersect, Z and M values are interpolated at intersection points.

This function works well with 3D terrain-like geometries (2.5D) but is not designed for vertical surfaces like walls.

Availability: 3.6.0 - requires SFCGAL >= 2.1.0

Cette méthode nécessite le backend SFCGAL.

Cette fonction prend en charge la 3D et ne supprime pas l'indice z.

Cette fonction prend en charge les coordonnées M.

Paramètres

Return Value

Returns a simplified geometry with preserved Z and M values.

Exemples

This example simplifies a polygon with a threshold of 0.5.

SELECT ST_AsText(CG_Simplify(ST_GeomFromText('POLYGON((0 0, 0 1, 0.1 1, 0.2 1, 0.3 1, 0.4 1, 0.5 1, 1 1, 1 0, 0 0))'), 0.5));

Simplify a 3D terrain geometry while preserving topology and Z values.

SELECT ST_AsText(CG_Simplify(ST_GeomFromText('LINESTRING Z(0 0 0, 0 1 1, 0.1 1 1, 0.2 1 1, 0.3 1 1, 1 1 2)'), 0.2, true));

Simplify a geometry with both Z and M values.

SELECT ST_AsText(CG_Simplify(ST_GeomFromText('LINESTRING ZM(0 0 0 1, 0 1 1 2, 0.1 1 1 3, 0.2 1 1 4, 0.3 1 1 5, 1 1 2 6)'), 0.2));

Simplify two geometries together, preserving Z and M values without preserving topology.

SELECT ST_AsText(CG_Simplify('GEOMETRYCOLLECTION ZM(LINESTRING ZM(-1 -1 3 4, 0 0 10 100, 1 1 20 200, 0 2 15 150, 0 5 30 300, 2 19 25 250, -4 20 15 150), POLYGON ZM((0 0 10 100, 1 1 20 200, 0 2 15 150, 0 5 30 300, 2 19 25 250, -4 20 15 150, 0 0 10 100)))', 2, false));

Simplify two geometries together, preserving Z and M values and topology.

SELECT ST_AsText(CG_Simplify('GEOMETRYCOLLECTION ZM(LINESTRING ZM(-1 -1 3 4, 0 0 10 100, 1 1 20 200, 0 2 15 150, 0 5 30 300, 2 19 25 250, -4 20 15 150), POLYGON ZM((0 0 10 100, 1 1 20 200, 0 2 15 150, 0 5 30 300, 2 19 25 250, -4 20 15 150, 0 0 10 100)))', 2, true));

WITH depts_pds as (SELECT ST_GeomFromText('GEOMETRYCOLLECTION(
POLYGON((88.46 158.85,90.77 171.54,147.31 173.85,146.15 145,173.85 119.62,146.15 103.46,112.69 118.46,91.92 93.08,65.38 101.15,34.23 121.92,41.15 142.69,49.23 143.85,88.46 158.85)),
POLYGON((112.69 118.46,146.15 103.46,190 60.77,185.38 43.46,126.54 26.15,83.85 28.46,67.69 64.23,43.46 58.46,10 83.85,34.23 121.92,65.38 101.15,91.92 93.08,112.69 118.46)))
') as geom)
SELECT geom FROM depts_pds;
        

WITH depts_pds as (SELECT ST_GeomFromText('GEOMETRYCOLLECTION(
POLYGON((88.46 158.85,90.77 171.54,147.31 173.85,146.15 145,173.85 119.62,146.15 103.46,112.69 118.46,91.92 93.08,65.38 101.15,34.23 121.92,41.15 142.69,49.23 143.85,88.46 158.85)),
POLYGON((112.69 118.46,146.15 103.46,190 60.77,185.38 43.46,126.54 26.15,83.85 28.46,67.69 64.23,43.46 58.46,10 83.85,34.23 121.92,65.38 101.15,91.92 93.08,112.69 118.46)))
') as geom)
SELECT (ST_Dump(CG_Simplify(geom, 0.5, true))).geom FROM depts_pds;
        

WITH depts_pds as (SELECT ST_GeomFromText('GEOMETRYCOLLECTION(
POLYGON((88.46 158.85,90.77 171.54,147.31 173.85,146.15 145,173.85 119.62,146.15 103.46,112.69 118.46,91.92 93.08,65.38 101.15,34.23 121.92,41.15 142.69,49.23 143.85,88.46 158.85)),
POLYGON((112.69 118.46,146.15 103.46,190 60.77,185.38 43.46,126.54 26.15,83.85 28.46,67.69 64.23,43.46 58.46,10 83.85,34.23 121.92,65.38 101.15,91.92 93.08,112.69 118.46)))
') as geom)
SELECT (ST_Dump(CG_Simplify(geom, 0.5, false))).geom FROM depts_pds;
      

Voir aussi

ST_Simplify, ST_SimplifyPreserveTopology