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SE_LocateAlong()
SE_LocateAlong() takes a geometry object and a measure to return as an
ST_MultiPoint the set of points found having that measure.
Syntax
SE_LocateAlong(g1 ST_Geometry, m1 double precision)
Return Type
ST_Geometry
Example
The locatealong_test table is created with two columns: the gid column uniquely
identifies each row, and the g1 ST_Geometry column stores sample geometry:
CREATE TABLE locatealong_test (gid integer,
g1 ST_Geometry);
The following INSERT statements insert two rows. The first is a multilinestring,
while the second is a multipoint:
INSERT INTO locatealong_test VALUES(
1,
ST_MLineFromText('multilinestring m ((10.29 19.23 5,23.82 20.29
6,30.19 18.47 7,45.98 20.74 8),(23.82 20.29 6,30.98 23.98 7,42.92
25.98 8))', 1000)
);
INSERT INTO locatealong_test VALUES(
2,
ST_MPointFromText('multipoint m (10.29 19.23 5,23.82 20.29
6,30.19 18.47 7,45.98 20.74 8,23.82 20.29 6,30.98 23.98 7,42.92
25.98 8)', 1000)
);
In this query, the SE_LocateAlong() function finds points whose measure is 6.5.
The first row returns an ST_MultiPoint containing two points. However, the second
row returns an empty point. For linear features (geometry with a dimension
greater than 0), SE_LocateAlong() can interpolate the point, but for multipoints the
target measure must match exactly:
SELECT gid, SE_locatealong(g1,6.5) Geometry
FROM locatealong_test;
gid
1
geometry 1000 MULTIPOINT M (27.005 19.38 6.5, 27.4 22.135 6.5)
gid
2
geometry 1000 POINT M EMPTY
In this query, the SE_LocateAlong() function returns a multipoint for both rows.
The target measure of 7 matches measures in the multilinestring and multipoint
source data:
SELECT gid, SE_locatealong(g1,7) Geometry
FROM locatealong_test;
gid
1
geometry 1000 MULTIPOINT M (30.19 18.47 7, 30.98 23.98 7)
Chapter 8. SQL Functions
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