Name
ST_StartM — Returns the M coordinate of the first point of a LineString, CircularLineString, or NURBSCurve.
Synopsis
float8 ST_StartM(geometry geom);
Description
Returns the M coordinate of the first point of a LINESTRING,
CIRCULARLINESTRING, or NURBSCURVE geometry.
Returns NULL if the input geometry does not have an M dimension or
is not a LINESTRING, CIRCULARLINESTRING, or NURBSCURVE.
This method supports Circular Strings and Curves.
Examples
Start M value of a LineString
Code
SELECT ST_StartM('LINESTRING M(0 0 10,1 1 20,2 0 30)'::geometry);
Output
10
Figure
Start M value of a CircularString
Code
SELECT ST_StartM('CIRCULARSTRING M(0 0 5,1 1 10,2 0 15)'::geometry);
Output
5
Figure
Start M value of a NURBSCurve
Code
SELECT ST_StartM('NURBSCURVE M(2, (0 0 100, 1 1 200, 2 0 300))'::geometry);
Output
100
Figure
Geometry without M dimension returns NULL
Code
SELECT ST_StartM('LINESTRING(0 0,1 1)'::geometry) IS NULL AS is_null;
Output
t
Figure