ST_IsValid
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Name

ST_IsValid — Tests if a geometry is well-formed in 2D.

Synopsis

boolean ST_IsValid(geometry g);

boolean ST_IsValid(geometry g, integer flags);

Descrizione

Tests if an ST_Geometry value is well-formed and valid in 2D according to the OGC rules. For geometries with 3 and 4 dimensions, the validity is still only tested in 2 dimensions. For geometries that are invalid, a PostgreSQL NOTICE is emitted providing details of why it is not valid.

For the version with the flags parameter, supported values are documented in ST_IsValidDetail This version does not print a NOTICE explaining invalidity.

For more information on the definition of geometry validity, refer to Section 4.4, “Geometry Validation”

[Note]

SQL-MM defines the result of ST_IsValid(NULL) to be 0, while PostGIS returns NULL.

Eseguito dal modulo GEOS.

The version accepting flags is available starting with 2.0.0.

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

Questo metodo implementa la specifica SQL/MM. SQL-MM 3: 5.1.9

[Note]

Neither OGC-SFS nor SQL-MM specifications include a flag argument for ST_IsValid. The flag is a PostGIS extension.

Esempi

SELECT ST_IsValid(ST_GeomFromText('LINESTRING(0 0, 1 1)')) As good_line,
        ST_IsValid(ST_GeomFromText('POLYGON((0 0, 1 1, 1 2, 1 1, 0 0))')) As bad_poly
--results
NOTICE:  Self-intersection at or near point 0 0
 good_line | bad_poly
-----------+----------
 t         | f