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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.

Identifying Tight Radius Curves sections within LineString geometry data

Wednesday May 04 2011 at 12:20

Sometimes it is a data quality requirement for linear data (roads, pipelines, transmission lines) that curves within the lines must have a radius greater than a particular amount.

Recently a customer asked me to write some TSQL functions to help them run data quality checks over linear data loaded into a SQL Server 2008 geometry column directly from a CAD package.

The function I created is called CheckRadii and is as follows:

/** ----------------------------------------------------------------------------------------
  * @function   : CheckRadii
  * @precis     : Function that checks vertices in a linestring/multilinestring to see if
  *               the circular arc they describe have radius less than the provided amount.
  *               Each set of three vertices (which could be overlapping) that fail the test
  *               are written to a single MultiPoint object. If no circular arcs in the linestring
  *               describe a circle with radius less than the required amount a NULL geometry is returned.
  *               If another other than a (Multi)linestring is provided it is returned as is.
  * @version    : 1.0
  * @usage      : Function CheckRadii(@p_geom       geometry,
  *                                   @p_min_radius Float,
  *                                   @p_precision  int )
  *                 Return geometry
  *               eg SELECT [CheckRadii](geometry::STGeomFromText('LINESTRING(0.0 0.0,10.0 0.0,10.0 10.0)',0), 15.0,3).STAsText();
  * @param      : p_geom       : Projected (Multi)Linestring geometry
  * @paramtype  : p_geom       : geometry
  * @param      : p_min_radius : A not null value that describes the minimum radiue of any arc within the linestring.
  * @paramtype  : p_min_radius : Float
  * @param      : p_precision  : Precision of any XY value ie number of significant digits. If null then 3 is assumed (ie 1 mm): 3456.2345245 -> 3456.235 
  * @paramtype  : p_precision  : Int
  * @return     : mpoint_geom  : Projected 2D MultiPoint geometry
  * @rtnType    : mpoint_geom  : geometry
  * @note       : Supplied geometry must not be geographic: function only guaranteed for projected data.
  * @note       : Does not honour dimensions over 2.
  * @history    : Simon Greener - May 2011 - Original coding.
  * @copyright  : Licensed under a Creative Commons Attribution-Share Alike 2.5 Australia License. (http://creativecommons.org/licenses/by-sa/2.5/au/)
CREATE FUNCTION [CheckRadii](@p_geom       geometry,
                             @p_min_radius Float,
                             @p_precision  int )
RETURNS geometry 

And can be called as follows:

SELECT [CheckRadii](geometry::STGeomFromText('MULTILINESTRING(
(0.0 0.0,10.0 0.0,10.0 10.0),
(20.0 0.0,30.0 0.0,30.0 10.0))',0), 15.0,3).STAsText(); 

Some examples of running this against test road data with a 15.0 meter radius and precision of 3 (ie 1 mm) are as follows.

If anyone wishes for a similar function to be written for them, please let me know.

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