MULTILINESTRING

A MULTILINESTRING is a collection of LineStrings. MultiLineStrings are useful for gathering a group of LineStrings into one geometry. For example, you may want to gather the LineStrings denoting all of the roads in a particular municipality.

New in v21.1: You can also store a MULTILINESTRING with the following additional dimensions:

  • A third dimension coordinate Z (MULTILINESTRINGZ).
  • A measure coordinate M (MULTILINESTRINGM).
  • Both a third dimension and a measure coordinate (MULTILINESTRINGZM).

The Z and M dimensions can be accessed or modified using a number of built-in functions, including:

  • ST_Z
  • ST_M
  • ST_Affine
  • ST_Zmflag
  • ST_MakePoint
  • ST_MakePointM
  • ST_Force3D
  • ST_Force3DZ
  • ST_Force3DM
  • ST_Force4D
  • ST_Snap
  • ST_SnapToGrid
  • ST_RotateZ
  • ST_AddMeasure

Note that CockroachDB's spatial indexing is still based on the 2D coordinate system. This means that:

  • The Z/M dimension is not index accelerated when using spatial predicates.
  • Some spatial functions ignore the Z/M dimension, with transformations discarding the Z/M value.

Examples

Well known text

A MultiLineString can be created from SQL by calling the st_geomfromtext function on a MultiLineString definition expressed in the Well Known Text (WKT) format.

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SELECT ST_GeomFromText('MULTILINESTRING((0 0, 1440 900), (800 600, 200 400))');
                                                                                     st_geomfromtext
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  0105000000020000000102000000020000000000000000000000000000000000000000000000008096400000000000208C4001020000000200000000000000000089400000000000C0824000000000000069400000000000007940
(1 row)

SQL

A MultiLineString can be created from SQL by calling an aggregate function such as ST_Collect or ST_Union on a column that contains LineString geometries. In the example below, we will build a MultiLineString from several LineStrings.

First, insert the LineStrings:

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CREATE TABLE tmp_linestrings (id INT8 default unique_rowid(), geom GEOMETRY);

INSERT INTO tmp_linestrings (geom)
VALUES
(st_geomfromtext('SRID=4326;LINESTRING(-88.243385 40.116421, -87.906471 43.038902, -95.992775 36.153980)')),
(st_geomfromtext('SRID=4326;LINESTRING(-75.704722 36.076944, -95.992775 36.153980, -87.906471 43.038902)')),
(st_geomfromtext('SRID=4326;LINESTRING(-76.8261 42.1727,  -75.6608 41.4102,-73.5422 41.052, -73.929 41.707,  -76.8261 42.1727)'));

Next, build a MultiLineString from the individual LineStrings using ST_Collect, and check the output with ST_GeometryType to verify that it is indeed a MultiLineString:

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SELECT ST_GeometryType(st_collect(geom)) AS output FROM tmp_linestrings;
        output
----------------------
  ST_MultiLineString
(1 row)

Finally, drop the temporary table:

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DROP TABLE tmp_linestrings;

See also

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