H2GIS

Fork me on GitHub

ST_IsValidReason

Signatures

VARCHAR ST_IsValidReason(GEOMETRY geom);
VARCHAR ST_IsValidReason(GEOMETRY geom, INT selfTouchValid);

Description

Returns a string stating if a geom is valid or a reason why if it is not.

Optional variable selfTouchValid sets whether polygons using self-touching rings to form holes are reported as valid. If this flag is set, the following self-touching conditions are treated as being valid:

  • The shell ring self-touches to create a hole touching the shell
  • A hole ring self-touches to create two holes touching at a point

The default of 0 (following the OGC SFS standard) is that this condition is not valid. Set it to 1 to consider it valid (c.f. ESRI SDE model).

We have the following equivalence:

ST_IsValidReason(geom) = ARRAY_GET(ST_IsValidDetail(geom), 2)

Examples

SELECT ST_IsValidReason('POLYGON((210 440, 134 235, 145 233,
                                  310 200, 340 360, 210 440))');
-- Answer: Valid Geometry

SELECT ST_IsValidReason('POLYGON((0 0, 10 0, 10 5, 6 -2, 0 0))');
-- Answer: Self-intersection at or near
--         POINT(7.142857142857143, 0.0, NaN)

SELECT ST_IsValidReason('POLYGON((1 1, 1 6, 5 1, 1 1),
                                 (3 4, 3 5, 4 4, 3 4))', 0);
-- Answer: Hole lies outside shell at or near POINT(3.0, 4.0, NaN)

-- The next two examples show that the validation model we choose
-- is important.
SELECT ST_IsValidReason(
            'POLYGON((3 0, 0 3, 6 3, 3 0, 4 2, 2 2, 3 0))', 0);
-- Answer: Ring Self-intersection at or near POINT(3.0, 0.0, NaN)

SELECT ST_IsValidReason(
            'POLYGON((3 0, 0 3, 6 3, 3 0, 4 2, 2 2, 3 0))', 1);
-- Answer: Valid Geometry

See also