名称
ST_Snap — 将输入几何体的线段和顶点捕捉到参考几何体的顶点。
大纲
geometry ST_Snap(geometry input, geometry reference, float tolerance);
描述
将一个几何体的顶点和边捕捉到另一个几何体的顶点。捕捉距离公差用于控制执行捕捉的位置。 结果几何体是顶点被捕捉的输入几何体。 如果没有发生捕捉，则输入几何体将原样返回。
将一个几何体捕捉到另一个几何体可以通过消除几何重合的边（这会在节点和相交计算期间引起问题）来提高叠加操作的可靠性。
过多的捕捉可能会导致创建无效的拓扑，因此使用启发式方法确定捕捉顶点的数量和位置，以确定何时可以安全捕捉。 然而，这可能会导致一些潜在的捕捉被忽略。
![[注意]](../images/note.png)
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返回的几何图形可能已失去其简单性（请参阅ST_IsSimple）或可能无效（请参阅ST_IsValid）。 |
这个函数是由 GEOS 模块执行的。
可用性: 2.0.0
示例
A MultiPolygon snapped to a LineString at 1.01 times their distance.
Code
SELECT ST_Snap(poly, line, ST_Distance(poly, line)*1.01) AS polysnapped
FROM (SELECT
ST_GeomFromText('MULTIPOLYGON(
((26 125,26 200,126 200,126 125,26 125 ),
( 51 150,101 150,76 175,51 150 )),
(( 151 100,151 200,176 175,151 100 )))') As poly,
ST_GeomFromText('LINESTRING (5 107,54 84,101 100)') As line
) As foo;
栅格输出
MULTIPOLYGON(((26 125,26 200,126 200,126 125,101 100,26 125), (51 150,101 150,76 175,51 150)),((151 100,151 200,176 175,151 100)))
Figure
A MultiPolygon snapped to a LineString at 1.25 times their distance.
Code
SELECT ST_Snap(poly, line, ST_Distance(poly, line)*1.25) AS polysnapped
FROM (SELECT
ST_GeomFromText('MULTIPOLYGON(
(( 26 125,26 200,126 200,126 125,26 125 ),
( 51 150,101 150,76 175,51 150 )),
(( 151 100,151 200,176 175,151 100 )))') As poly,
ST_GeomFromText('LINESTRING (5 107,54 84,101 100)') As line
) As foo;
栅格输出
MULTIPOLYGON(((5 107,26 200,126 200,126 125,101 100,54 84,5 107), (51 150,101 150,76 175,51 150)),((151 100,151 200,176 175,151 100)))
Figure
The LineString snapped to the original MultiPolygon at 1.01 times their distance.
Code
SELECT ST_Snap(line, poly, ST_Distance(poly, line)*1.01) AS linesnapped
FROM (SELECT
ST_GeomFromText('MULTIPOLYGON(
((26 125,26 200,126 200,126 125,26 125),
(51 150,101 150,76 175,51 150 )),
((151 100,151 200,176 175,151 100)))') As poly,
ST_GeomFromText('LINESTRING (5 107,54 84,101 100)') As line
) As foo;
栅格输出
LINESTRING(5 107,26 125,54 84,101 100)
Figure
The LineString snapped to the original MultiPolygon at 1.25 times their distance.
Code
SELECT ST_Snap(line, poly, ST_Distance(poly, line)*1.25) AS linesnapped
FROM (SELECT
ST_GeomFromText('MULTIPOLYGON(
(( 26 125,26 200,126 200,126 125,26 125 ),
(51 150,101 150,76 175,51 150 )),
((151 100,151 200,176 175,151 100 )))') As poly,
ST_GeomFromText('LINESTRING (5 107,54 84,101 100)') As line
) As foo;
栅格输出
LINESTRING(26 125,54 84,101 100)
Figure