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

Returns the point or multipoint geometry containing all elements in a measured geometry where the M coordinate equals the specified measure value.

Syntax

geometry ST_LocateAlong(geometry ageomWithMeasure, float8 aMeasure, float8 offset);

Parameter	Type	Description
`ageomWithMeasure`	geometry	The measured geometry to search. Must include an M component, such as `LINESTRINGM`, `MULTILINESTRINGM`, or `MULTIPOINTM`. Polygon geometries are not supported.
`aMeasure`	float8	The M coordinate value to locate.
`offset`	float8	The lateral offset distance applied to each result point, in the same units as the geometry. A positive value shifts the point to the left of the input line; a negative value shifts it to the right along the input line.

Pass only geometries that include an M component. Polygon geometries are not supported.

When the specified measure appears at more than one location, the function returns a MULTIPOINT M containing all matches.
A non-zero offset shifts each result point to the left or to the right along the input line by the specified distance.

Find all points in a MULTIPOINTM geometry where M equals 3:

SELECT ST_AsText(
  ST_LocateAlong(
    ST_GeomFromText('MultiPointM((1 2 3),(5 4 3),(4 5 6))'),
    3
  )
);

Result:

         st_astext
----------------------------
 MULTIPOINT M (1 2 3,5 4 3)
(1 row)

Both (1 2 3) and (5 4 3) have M = 3 and are included in the output. The point (4 5 6) has M = 6 and is excluded.