ST_IsValid — Tests if a geometry is well-formed in 2D.
boolean ST_IsValid(geometry g
boolean ST_IsValid(geometry g, integer flags
Test if an ST_Geometry value is well-formed in 2D according to the OGC rules. For geometries that are invalid, the PostgreSQL NOTICE will provide details of why it is not valid. For geometries with 3 and 4 dimensions, the validity still only tested in 2 dimensions.
For the version with flags,
flags 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 "Ensuring OpenGIS compliancy of geometries"
SQL-MM defines the result of ST_IsValid(NULL) to be 0, while PostGIS returns NULL.
Performed by the GEOS module.
The version accepting flags is available starting with 2.0.0.
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This method implements the SQL/MM specification. SQL-MM 3: 5.1.9
Neither OGC-SFS nor SQL-MM specifications include a flag argument for ST_IsValid. The flag is a PostGIS extension.
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