The ST_M function takes a point as an
input parameter and returns its measure (M) coordinate. You can optionally
indicate an M coordinate as input parameter in addition to the point
and the function returns the point itself with its M coordinate set
to the given value.
If the specified M coordinate is null, then the M coordinate
of the point is removed.
If the specified point is null or is
empty, then null is returned.
This function can also be called
as a method.
Syntax
Parameters
point
A value of type ST_Point for which the M coordinate is returned
or modified.
m_coordinate
A value of type DOUBLE that represents the new M coordinate for point.
If m_coordinate is
null, then the M coordinate is removed from point.
Return types
DOUBLE, if m_coordinate is not specified
db2gse.ST_Point, if m_coordinate is specified
Examples
Example 1
This example illustrates the use of the ST_M function. Three
points are created and inserted into the SAMPLE_POINTS table. They
are all in the spatial reference system that has an ID of 1.
SET CURRENT FUNCTION PATH = CURRENT FUNCTION PATH, db2gse
CREATE TABLE sample_points (id INTEGER, geometry ST_Point)
INSERT INTO sample_points
VALUES (1, ST_Point (2, 3, 32, 5, 1))
INSERT INTO sample_points
VALUES (2, ST_Point (4, 5, 20, 4, 1))
INSERT INTO sample_points
VALUES (3, ST_Point (3, 8, 23, 7, 1))
Example 2
This example finds the M coordinate of the points in the SAMPLE_POINTS
table.
SELECT id, ST_M (geometry) M_COORD
FROM sample_points
Results:
ID M_COORD
----------- ------------------------
1 +5.00000000000000E+000
2 +4.00000000000000E+000
3 +7.00000000000000E+000
Example 3
This example returns one of the points with its M coordinate
set to 40.
SELECT id, CAST (ST_AsText (ST_M (geometry, 40) )
AS VARCHAR(60) ) M_COORD_40
FROM sample_points
WHERE id=3
Results:
ID M_COORD_40
---------- -------------------------------------------------------
3 POINT ZM (3.00000000 8.00000000 23.00000000 40.00000000)