名称
CG_StraightSkeleton — 从几何体计算直骨架
大纲
geometry CG_StraightSkeleton(geometry geom, boolean use_distance_as_m = false);
描述
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.
可用性：3.5.0
要使用任意参数 use_distance_as_m，需要 SFCGAL >= 1.3.8
该方法需要SFCGAL后端。
该函数支持 3d 并且不会丢失 z-index。
该函数支持多面体曲面。
此函数支持三角形和不规则三角网面 (TIN)。
示例
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;
栅格输出
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
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;
栅格输出
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
请注意，若合法输入中的环仅在单个点处相接，将会引发错误。
Code
SELECT CG_StraightSkeleton('POLYGON((0 0,3 0,3 3,0 3,0 0),(0 0,1 2,2 1,0 0))'));
栅格输出
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.