Name
ST_SetStartM — Sets the M coordinate of the first point of a LineString, CircularLineString, or NURBSCurve.
Synopsis
geometry ST_SetStartM(geometry geom, float8 m);
Description
Returns a copy of the input LINESTRING,
CIRCULARLINESTRING, or NURBSCURVE geometry
with the M coordinate of the first point set to the specified value.
If the input geometry does not have an M dimension, it will be added.
Returns NULL if the input
is not a LINESTRING, CIRCULARLINESTRING, or NURBSCURVE.
This method supports Circular Strings and Curves.
Examples
Set start M value of a LineString
Code
SELECT ST_SetStartM('LINESTRING M(0 0 10,1 1 20,2 0 30)'::geometry, 100);
Output
LINESTRING M (0 0 100,1 1 20,2 0 30)
Figure
Add M dimension and set start M value
Code
SELECT ST_SetStartM('LINESTRING(0 0,1 1,2 0)'::geometry, 50);
Output
LINESTRING M (0 0 50,1 1 0,2 0 0)
Figure
Set start M value of a CircularString
Code
SELECT ST_SetStartM('CIRCULARSTRING M(0 0 5,1 1 10,2 0 15)'::geometry, 99);
Output
CIRCULARSTRING M (0 0 99,1 1 10,2 0 15)
Figure
Set start M value of a NURBSCurve
Code
SELECT ST_SetStartM('NURBSCURVE M(2, (0 0 100, 1 1 200, 2 0 300))'::geometry, 500);
Output
NURBSCURVE M (DEGREE 2,CONTROLPOINTS M (NURBSPOINT(WEIGHTEDPOINT M (0 0 500),WEIGHT 1), NURBSPOINT(WEIGHTEDPOINT M (1 1 200),WEIGHT 1), NURBSPOINT(WEIGHTEDPOINT M (2 0 300),WEIGHT 1)),KNOTS (KNOT(0,3), KNOT(1,3)))
Figure