ST_LineMerge

ST_LineMerge
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Name

ST_LineMerge — Return the lines formed by sewing together a MultiLineString.

Synopsis

geometry ST_LineMerge(geometry amultilinestring);

geometry ST_LineMerge(geometry amultilinestring, boolean directed);

Description

Returns a LineString or MultiLineString formed by joining together the line elements of a MultiLineString. Lines are joined at their endpoints at 2-way intersections. Lines are not joined across intersections of 3-way or greater degree.

If directed is TRUE, then ST_LineMerge will not change point order within LineStrings, so lines with opposite directions will not be merged


	Only use with MultiLineString/LineStrings. Other geometry types return an empty GeometryCollection

Performed by the GEOS module.

Enhanced: 3.3.0 accept a directed parameter.

Requires GEOS >= 3.11.0 to use the directed parameter.

Availability: 1.1.0


	This function strips the M dimension.

Examples

Cardinality 2

Nodes with cardinality 2 are merged away.

Code

SELECT ST_LineMerge('MULTILINESTRING((10 160,60 120),(120 140,60 120),(120 140,180 120))'
);

Output

LINESTRING(10 160,60 120,120 140,180 120)

010200000004000000000000000000244000000000000064400000000000004E400000000000005E400000000000005E40000000000080614000000000008066400000000000005E40

Figure

Cardinality 3 or More

Lines are not merged across intersections with degree > 2.

Code

SELECT ST_LineMerge('MULTILINESTRING((10 160,60 120),(120 140,60 120),(120 140,180 120),(100 180,120 140))'
);

Output

MULTILINESTRING((10 160,60 120,120 140),(100 180,120 140),(120 140,180 120))

010500000003000000010200000003000000000000000000244000000000000064400000000000004E400000000000005E400000000000005E400000000000806140010200000002000000000000000000594000000000008066400000000000005E4000000000008061400102000000020000000000000000005E40000000000080614000000000008066400000000000005E40

Figure

Non-Touching Lines

If merging is not possible due to non-touching lines, the original MultiLineString is returned.

Code

SELECT ST_LineMerge('MULTILINESTRING((-29 -27,-30 -29.7,-36 -31,-45 -33),(-45.2 -33.2,-46 -32))'
);

Output

MULTILINESTRING((-45.2 -33.2,-46 -32),(-29 -27,-30 -29.7,-36 -31,-45 -33))

0105000000020000000102000000020000009A999999999946C09A999999999940C000000000000047C000000000000040C00102000000040000000000000000003DC00000000000003BC00000000000003EC03333333333B33DC000000000000042C00000000000003FC000000000008046C000000000008040C0

Figure

Directed Parameter

Lines with opposite directions are not merged if directed is TRUE.

Code

SELECT ST_LineMerge('MULTILINESTRING((60 30,10 70),(120 50,60 30),(120 50,180 30))',
TRUE);

Output

MULTILINESTRING((120 50,60 30,10 70),(120 50,180 30))

0105000000020000000102000000030000000000000000005E4000000000000049400000000000004E400000000000003E40000000000000244000000000008051400102000000020000000000000000005E40000000000000494000000000008066400000000000003E40

Figure

Z-dimension Handling

Code

SELECT ST_LineMerge('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))'
        );

Output

LINESTRING Z (-30 -29.7 5,-29 -27 11,-30 -29.7 10,-36 -31 5,-45 -33 1,-46 -32 11)

0102000080060000000000000000003EC03333333333B33DC000000000000014400000000000003DC00000000000003BC000000000000026400000000000003EC03333333333B33DC0000000000000244000000000000042C00000000000003FC0000000000000144000000000008046C000000000008040C0000000000000F03F00000000000047C000000000000040C00000000000002640

Figure

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Name

Synopsis

Description

Examples

Cardinality 2

Cardinality 3 or More

Non-Touching Lines

Directed Parameter

Z-dimension Handling

See Also