名称
CG_ApproximateMedialAxis — 计算几何区域的近似中轴。
大纲
geometry CG_ApproximateMedialAxis(geometry geom);
geometry CG_ApproximateMedialAxis(geometry geom, boolean projected);
描述
基于直骨架，返回实际输入的近似中心轴。如果在支持的版本（1.2.0+）下构建，将使用 SFCGAL 特有的 API；否则，此函数将是 CG_StraightSkeleton（较慢的情况）函数的封装。
When projected is true, free endpoints of the medial axis are extended to reach the polygon boundary (projected medial axis). Requires SFCGAL 2.3.0+. When built against an older SFCGAL version, a notice is emitted and the non-projected result is returned instead.
可用性：3.5.0
Availability: 3.7.0 - projected parameter. Requires SFCGAL >= 2.3.0 for projected result; falls back to non-projected with a notice on older versions.
![[注意]](../images/note.png)
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此函数忽略 Z 维度。 即使在 3D 几何体上使用时，它也始终给出 2D 结果。 |
该方法需要SFCGAL后端。
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
A polygon and its approximate medial axis.
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 polygon AS input_polygon,
CG_ApproximateMedialAxis(polygon) AS medial_axis
FROM data;
POLYGON((190 190,10 190,10 10,190 10,190 20,160 30,60 30,60 130,190 140,190 190)) | MULTILINESTRING((184.189 15.811,158.377 20),(50 20,158.377 20),(50 20,35 35),(35 153.151,35 35),(35 153.151,40.697 159.303),(164.04 164.04,40.697 159.303))
This example computes the projected medial axis with free endpoints extended to the polygon boundary.
SELECT CG_ApproximateMedialAxis('POLYGON((0 0,2 0,2 1,0 1,0 0))', true);
MULTILINESTRING((0 0.5,0.5 0.5,1.5 0.5,2 0.5))