CG_StraightSkeleton
Précédent  8.3. Fonctions de traitement et de relation SFCGAL  Suivant

Nom

CG_StraightSkeleton — Calcule un squelette (straight skeleton) à partir d'une géométrie

Synopsis

geometry CG_StraightSkeleton(geometry geom, boolean use_distance_as_m = false);

Description

Computes the straight skeleton of a polygon by tracing the inward propagation of its edges. When use_distance_as_m is true, the M coordinate of each output point stores its distance from the input boundary.

Disponibilité : 3.5.0

Nécessite SFCGAL >= 1.3.8 pour l'option use_distance_as_m

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 surfaces Polyhedral.

Cette fonction prend en charge les triangles et les réseaux irréguliers triangulés (TIN).

Exemples

Code
WITH data AS (
  SELECT 'POLYGON((190 190,10 190,10 10,190 10,190 20,160 30,60 30,60 130,190 140,190 190))'::geometry AS polygon
)
SELECT CG_StraightSkeleton(polygon) AS straight_skeleton
FROM data;
Export de raster
MULTILINESTRING((190 190,164.03987973986756 164.03987973986756),(10 190,40.697077206292434 159.30292279370755),(10 10,35 35),(190 10,184.18861169915812 15.811388300841896),(190 20,184.18861169915812 15.811388300841896),(160 30,158.3772233983162 20),(60 30,50 20),(60 130,35 153.15077848154866),(190 140,164.03987973986756 164.03987973986756),(184.18861169915812 15.811388300841896,158.3772233983162 20),(50 20,158.3772233983162 20),(50 20,35 35),(35 153.15077848154866,35 35),(35 153.15077848154866,40.697077206292434 159.30292279370755),(164.03987973986756 164.03987973986756,40.697077206292434 159.30292279370755))
Figure
Geometry figure for visual-cg-straightskeleton-01
Code
WITH data AS (
  SELECT 'POLYGON((0 0,1 0,1 1,0 1,0 0))'::geometry AS polygon
)
SELECT CG_StraightSkeleton(polygon, true) AS straight_skeleton_with_m
FROM data;
Export de raster
MULTILINESTRING M ((0 0 0,0.5 0.5 0.5),(1 0 0,0.5 0.5 0.5),(1 1 0,0.5 0.5 0.5),(0 1 0,0.5 0.5 0.5))
Figure
Geometry figure for visual-cg-straightskeleton-02

Note that valid inputs with rings that touch at a single point will raise an error.

Code
SELECT CG_StraightSkeleton('POLYGON((0 0,3 0,3 3,0 3,0 0),(0 0,1 2,2 1,0 0))'));
Export de raster
NOTICE:  During straight_skeleton(A) :
NOTICE:    with A: POLYGON((0/1 0/1,3/1 0/1,3/1 3/1,0/1 3/1,0/1 0/1),(0/1 0/1,1/1 2/1,2/1 1/1,0/1 0/1))
ERROR:  straight skeleton of Polygon with point touching rings is not implemented.