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);
描述
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.
此方法支持圆形字符串和曲线。
示例
Set start M value of a LineString
SELECT ST_AsText(ST_SetStartM('LINESTRING M(0 0 10, 1 1 20, 2 0 30)'::geometry, 100));
LINESTRING M (0 0 100,1 1 20,2 0 30)
Add M dimension and set start M value
SELECT ST_AsText(ST_SetStartM('LINESTRING(0 0, 1 1, 2 0)'::geometry, 50));
LINESTRING M (0 0 50,1 1 0,2 0 0)
Set start M value of a CircularString
SELECT ST_AsText(ST_SetStartM('CIRCULARSTRING M(0 0 5, 1 1 10, 2 0 15)'::geometry, 99));
CIRCULARSTRING M (0 0 99,1 1 10,2 0 15)
Set start M value of a NURBSCurve
SELECT ST_AsText(ST_SetStartM('NURBSCURVE M(2, (0 0 100, 1 1 200, 2 0 300))'::geometry, 500));
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)))