ST_LineMerge

Description

Returns a (set of) LineString(s) formed by sewing together the constituent line work of a MULTILINESTRING.

	Only use with MULTILINESTRING/LINESTRINGs. If you feed a polygon or geometry collection into this function, it will return an empty GEOMETRYCOLLECTION

Performed by the GEOS module.

Availability: 1.1.0

	Will strip the M dimension.

Examples

SELECT ST_AsText(ST_LineMerge(
ST_GeomFromText('MULTILINESTRING((-29 -27,-30 -29.7,-36 -31,-45 -33),(-45 -33,-46 -32))')
		)
);
st_astext
--------------------------------------------------------------------------------------------------
LINESTRING(-29 -27,-30 -29.7,-36 -31,-45 -33,-46 -32)
(1 row)

--If can't be merged - original MULTILINESTRING is returned
SELECT ST_AsText(ST_LineMerge(
ST_GeomFromText('MULTILINESTRING((-29 -27,-30 -29.7,-36 -31,-45 -33),(-45.2 -33.2,-46 -32))')
)
);
st_astext
----------------
MULTILINESTRING((-45.2 -33.2,-46 -32),(-29 -27,-30 -29.7,-36 -31,-45 -33))

-- example with Z dimension
SELECT ST_AsText(ST_LineMerge(
ST_GeomFromText('MULTILINESTRING((-29 -27 11,-30 -29.7 10,-36 -31 5,-45 -33 6), (-29 -27 12,-30 -29.7 5), (-45 -33 1,-46 -32 11))')
		)
);
st_astext
--------------------------------------------------------------------------------------------------
LINESTRING Z (-30 -29.7 5,-29 -27 11,-30 -29.7 10,-36 -31 5,-45 -33 1,-46 -32 11)
(1 row)
			

See Also

ST_Segmentize , ST_LineSubstring