ST_Difference
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Name

ST_Difference — Computes a geometry representing the part of geometry A that does not intersect geometry B.

Synopsis

geometry ST_Difference(geometry geomA, geometry geomB, float8 gridSize = -1);

Descrizione

Returns a geometry representing the part of geometry A that does not intersect geometry B. This is equivalent to A - ST_Intersection(A,B). If A is completely contained in B then an empty atomic geometry of appropriate type is returned.

[Note]

This is the only overlay function where input order matters. ST_Difference(A, B) always returns a portion of A.

If the optional gridSize parameter is given (GEOS-3.9.0 or higher required), all result vertices are guaranteed to fall on a grid of the specified size. For the operation to give predictable results all the input vertices must fall already on the specified grid, see ST_ReducePrecision.

Eseguito dal modulo GEOS

Enhanced: 3.1.0 accept a gridSize parameter.

Requires GEOS >= 3.9.0 to use the gridSize parameter.

Questo metodo implementa le OGC Simple Features Implementation Specification for SQL 1.1. s2.1.1.3

Questo metodo implementa la specifica SQL/MM. SQL-MM 3: 5.1.20

Questa funzione supporta il 3d e non distrugge gli z-index. However, the result is computed using XY only. The result Z values are copied, averaged or interpolated.

Esempi

The input linestrings

The difference of the two linestrings

The difference of 2D linestrings.

SELECT ST_AsText(
    ST_Difference(
            'LINESTRING(50 100, 50 200)'::geometry,
            'LINESTRING(50 50, 50 150)'::geometry
        )
    );

st_astext
---------
LINESTRING(50 150,50 200)

The difference of 3D points.

SELECT ST_AsEWKT( ST_Difference(
                   'MULTIPOINT(-118.58 38.38 5,-118.60 38.329 6,-118.614 38.281 7)' :: geometry,
                   'POINT(-118.614 38.281 5)' :: geometry
                  ) );

st_asewkt
---------
MULTIPOINT(-118.6 38.329 6,-118.58 38.38 5)