ST_FilterByM-ApsaraDB RDS(RDS)-阿里云帮助中心

Filters the vertexes of a geometry object by M coordinate range and returns a new geometry object.

Syntax

geometry ST_FilterByM(geometry geom, double precision min, double precision max, boolean returnM)

Parameter	Type	Default	Description
`geom`	geometry	—	The input geometry object.
`min`	double precision	null	The minimum M coordinate value. Vertexes with M coordinates below this value are filtered out.
`max`	double precision	null	The maximum M coordinate value. Vertexes with M coordinates above this value are filtered out. If null, only `min` takes effect.
`returnM`	boolean	false	Specifies whether to include M coordinates in the returned geometry object.

Returns a new geometry object containing only the vertexes whose M coordinate is ≥ min and ≤ max.
If max is null, only min is applied as the filter threshold.
If too few vertexes remain after filtering, the function returns an empty geometry object.
If the input geometry object does not contain enough points, ST_SimplifyVW returns a geometry object that contains enough points, while ST_FilterByM returns an empty geometry object.
If the input is a GeometryCollection, objects that do not contain enough points are ignored.
The returned geometry object preserves all dimensions of the input, including Z and M coordinates.
This function may return an invalid geometry object.

Filter by M coordinate range (M ≥ 2 and M ≤ 4)

SELECT ST_AsText(ST_FilterByM('LINESTRINGM(0 0 0,1 1 1,2 2 2,3 3 3)'::geometry,2,4,true));

Output:

         st_astext
----------------------------
 LINESTRING M (2 2 2,3 3 3)
(1 row)

Filter that produces an empty result (only one vertex matches, which is not enough to form a line)

SELECT ST_AsText(ST_FilterByM('LINESTRINGM(0 0 0,1 1 1,2 2 2,3 3 3)'::geometry,3,4,true));

Output:

     st_astext
--------------------
 LINESTRING M EMPTY
(1 row)