ST_M
Signature
DOUBLE ST_M(POINT geom);
Description
Return the M coordinate of a POINT (geom), or NULL if not available.
Warning
Input geometry must be a single POINT.
Examples
SELECT ST_M('POINT (2 1)');
-- Answer: Null
SELECT ST_M('POINT M(2 1 0)');
-- Answer: 0.0
Returning the M coordinate of the 3rd point of a POLYGON’s exterior ring
SELECT ST_M(ST_PointN(ST_ExteriorRing('POLYGON M((5 0 2, 7 0 4, 7 1 3, 5 1 6, 5 0 1))'), 3));
-- Answer: 3.0
Cases returning an error because geom is not a POINT
SELECT ST_M('MULTIPOINT M((4 4 3), (1 1 1), (1 0 2), (0 3 6))');
SELECT ST_M('LINESTRING M(2 1 0, 1 3 3, 5 2 1)');
SELECT ST_M('POLYGON M((5 0 2, 7 0 4, 7 1 3, 5 1 6, 5 0 1))');
SELECT ST_M('GEOMETRYCOLLECTION(
LINESTRING M(2 1 0, 1 3 3, 5 2 1),
MULTIPOINT M((4 4 3), (1 1 1), (1 0 2), (0 3 6)),
POLYGON M((1 2 2, 4 2 5, 4 6 3, 1 6 1, 1 2 1)))');