Nombre
ST_Snap — Ajusta segmentos y vértices de la geometría de entrada a vértices de una geometría de referencia.
Sinopsis
geometry ST_Snap(geometry input, geometry reference, float tolerance);
Descripción
Snaps the vertices and segments of a geometry to another Geometry's vertices. A snap distance tolerance is used to control where snapping is performed. The result geometry is the input geometry with the vertices snapped. If no snapping occurs then the input geometry is returned unchanged.
El ajustar una geometría a otra puede mejorar la robustez de las operaciones de superposición eliminando los bordes casi coincidentes (que causan problemas durante el cálculo de noding y de intersección).
Un ajuste excesivo puede resultar en la creación de una topología no válida, por lo que el número y la ubicación de los vértices ajustados se deciden usando heurísticas para determinar cuándo es seguro ajustar. Sin embargo, esto puede resultar en que algunos potenciales ajustes se omitan.
![[Nota]](../images/note.png)
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La geometría devuelta puede perder su simplicidad (ver ST_IsSimple) y su validez (ver ST_IsValid). |
Realizado por el módulo GEOS.
Disponibilidad: 2.0.0
Ejemplos
A MultiPolygon snapped to a LineString at 1.01 times their distance.
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;
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)))
A MultiPolygon snapped to a LineString at 1.25 times their distance.
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;
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)))
The LineString snapped to the original MultiPolygon at 1.01 times their distance.
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;
LINESTRING(5 107,26 125,54 84,101 100)
The LineString snapped to the original MultiPolygon at 1.25 times their distance.
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;
LINESTRING(26 125,54 84,101 100)