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All Blog Articles, Data Models and Free Source Code by Simon Greener, The SpatialDB Advisor is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

SQL Server Spatial: Extract LineStrings in GeometryCollection to create LineString

Wednesday August 01 2018 at 14:11

KeywordsExtract convert geometrycollection linestring multilinestring.
Summary

TSql STConvertToLineString function. Extracts linestring elements from GeometryCollection and returns either a LineString or a MultiLineString.

I had need today to create a function that extracts all linestring elements from a GeometryCollection and returns a LineString or a MultiLineString.

The function is called STConvertToLineString as is described as follows:

  1. CREATE FUNCTION [dbo].[STConvertToLineString]
  2. (
  3.   @p_geometry_collection geometry
  4. )
  5. RETURNS geometry
  6. AS
  7. BEGIN
  8.  ...
  9. END

Its documentation can be seen see here.

Here are some examples of how to use it:

  1. WITH gc AS (
  2.   SELECT geometry::STGeomFromText('GEOMETRYCOLLECTION(POINT(0 0), POLYGON((0 0,10 0,10 10,0 10,0 0)) )',0) AS geom
  3.    UNION ALL
  4.   SELECT geometry::STGeomFromText('GEOMETRYCOLLECTION(LINESTRING(0 0,20 0,20 20,0 20,0 0), POINT(0 0), POLYGON((0 0,10 0,10 10,0 10,0 0)) )',0) AS geom
  5.    UNION ALL
  6.   SELECT geometry::STGeomFromText('GEOMETRYCOLLECTION(LINESTRING(0 0,20 0,20 20,0 20,0 0), LINESTRING(1 1,2 2),LINESTRING(3 3,19 19),POINT(0 0), POLYGON((0 0,10 0,10 10,0 10,0 0)) )',0) AS geom
  7.    UNION ALL
  8.   SELECT geometry::STGeomFromText('GEOMETRYCOLLECTION(MULTILINESTRING((0 0,20 0),(20 20,0 20,0 0)), LINESTRING(1 1,2 2),LINESTRING(3 3,19 19),POINT(0 0), POLYGON((0 0,10 0,10 10,0 10,0 0)) )',0) AS geom
  9. )
  10. SELECT [dbo].[STConvertToLineString](geom).STAsText() AS geomWKT
  11.   FROM gc AS a
  12. GO
  13. -- Result
  14. geomWKT
  15. LINESTRING EMPTY
  16. LINESTRING (0 0, 20 0, 20 20, 0 20, 0 0)
  17. MULTILINESTRING ((0 0, 20 0, 20 20, 0 20, 0 0), (1 1, 2 2), (3 3, 19 19))
  18. MULTILINESTRING ((0 0, 20 0), (20 20, 0 20, 0 0), (1 1, 2 2), (3 3, 19 19))
I hope this function is of interest to someone.

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