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.

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

If the optional `gridSize` argument is provided, the inputs are snapped to a grid of the given size, and the result vertices are computed on that same grid. (Requires GEOS-3.9.0 or higher)

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)
```