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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.

Exposing JTS's MinimumBoundingCircle functionality

Sunday September 11 2011 at 07:55

KeywordsJTS ST_MinimumBoundingCircle
Summary

This article exposes Jts’s MinimumBoundingCircle for Oracle sdo_geometry users.

Today I decided to expose the Java Topology Suite’s (JTS) MinimumBoundingCircle functionality via the Spatial Companion For Oracle (SC4O) installer and package.

The MinimumBoundingCircle PL/SQL wrappers I have created are:

  1.   /**
  2.   * ST_MinimumBoundingCircle
  3.   * Computes the Minimum Bounding Circle (MBC) for the points in a Geometry.
  4.   * The MBC is the smallest circle which contains all the input points (this
  5.   * is sometimes known as the Smallest Enclosing Circle). This is equivalent
  6.   * to computing the Maximum Diameter of the input point set.
  7.   * @param p_geom      : sdo_geometry : first geometry subject to MBC calculation
  8.   * @param p_precision : int : number of decimal places of precision
  9.   * @return  circle    : sdo_geometry : Result of MBC calculation
  10.   * @author Martin Davis, JTS 1.12
  11.   * @history Simon Greener, September 2011, Original Coding of wrapper
  12.   * @copyright  : Licensed under a Creative Commons Attribution-Share Alike 2.5 Australia License.
  13.   *               http://creativecommons.org/licenses/by-sa/2.5/au/
  14.   **/
  15.   FUNCTION ST_MinimumBoundingCircle(p_geom      IN mdsys.sdo_geometry,
  16.                                     p_precision IN NUMBER)
  17.     RETURN mdsys.sdo_geometry deterministic;
  18. .
  19.   /**
  20.   * ST_MinimumBoundingCircle
  21.   * Computes the Minimum Bounding Circle (MBC) for the points in a Geometry.
  22.   * The MBC is the smallest circle which contains all the input points (this
  23.   * is sometimes known as the Smallest Enclosing Circle). This is equivalent
  24.   * to computing the Maximum Diameter of the input point set.
  25.   * @param p_geom      : sdo_geometry : first geometry subject to MBC calculation
  26.   * @param p_precision : int : number of decimal places of precision
  27.   * @param p_srid      : int : SRID of projected space in which actual overlay occurs before
  28.   *                            being projected back to p_geom1.sdo_srid.
  29.   * @return  circle    : sdo_geometry : Result of MBC calculation
  30.   * @author Martin Davis, JTS 1.12
  31.   * @history Simon Greener, September 2011, Original Coding of wrapper
  32.   * @copyright  : Licensed under a Creative Commons Attribution-Share Alike 2.5 Australia License.
  33.   *               http://creativecommons.org/licenses/by-sa/2.5/au/
  34.   **/
  35.   FUNCTION ST_MinimumBoundingCircle(p_geom      IN mdsys.sdo_geometry,
  36.                                     p_precision IN NUMBER,
  37.                                     p_srid      IN NUMBER )
  38.     RETURN mdsys.sdo_geometry deterministic;

Here are some examples.

  1. -- Point is returned as is
  2. SELECT SC4O.ST_MinimumBoundingCircle(sdo_geometry(2001,NULL,sdo_point_type(1,1,NULL),NULL,NULL),2) AS mbc FROM dual;
  3. .
  4. MBC
  5. ----------------------------------------------------------------------
  6. MDSYS.SDO_GEOMETRY(2001,NULL,MDSYS.SDO_POINT_TYPE(1,1,NULL),NULL,NULL)
  7. .
  8. -- Straight line defined by two points
  9. SELECT SC4O.ST_MinimumBoundingCircle(sdo_geometry('MULTIPOINT ((10 10), (20 20))',0),2) AS mbc  FROM dual;
  10. .
  11. MBC
  12. ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  13. MDSYS.SDO_GEOMETRY(2003,NULL,MDSYS.SDO_POINT_TYPE(15,15,7.07106781186548),MDSYS.SDO_ELEM_INFO_ARRAY(1,1003,4),MDSYS.SDO_ORDINATE_ARRAY(7.92893218813452,15,22.07106781186548,15,15,22.07106781186548))
  14. .
  15. -- Three Points In Line
  16. SELECT SC4O.ST_MinimumBoundingCircle(sdo_geometry('MULTIPOINT ((10 10), (20 20), (30 30))',0),2) AS mbc  FROM dual;
  17. .
  18. MBC
  19. -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  20. MDSYS.SDO_GEOMETRY(2003,NULL,MDSYS.SDO_POINT_TYPE(20,20,14.142135623731),MDSYS.SDO_ELEM_INFO_ARRAY(1,1003,4),MDSYS.SDO_ORDINATE_ARRAY(5.857864376269,20,34.142135623731,20,20,34.142135623731))
  21. .
  22. -- three points
  23. SELECT SC4O.ST_MinimumBoundingCircle(sdo_geometry('MULTIPOINT ((10 10), (20 20), (10 20))',0),2) AS mbc  FROM dual;
  24. .
  25. MBC
  26. ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  27. MDSYS.SDO_GEOMETRY(2003,NULL,MDSYS.SDO_POINT_TYPE(15,15,7.07106781186548),MDSYS.SDO_ELEM_INFO_ARRAY(1,1003,4),MDSYS.SDO_ORDINATE_ARRAY(7.92893218813452,15,22.07106781186548,15,15,22.07106781186548))
  28. .
  29. -- Triangle With Middle Point
  30. SELECT SC4O.ST_MinimumBoundingCircle(sdo_geometry('MULTIPOINT ((10 10), (20 20), (10 20), (15 19))',0),2) AS mbc  FROM dual;
  31. .
  32. MBC
  33. ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  34. MDSYS.SDO_GEOMETRY(2003,NULL,MDSYS.SDO_POINT_TYPE(15,15,7.07106781186548),MDSYS.SDO_ELEM_INFO_ARRAY(1,1003,4),MDSYS.SDO_ORDINATE_ARRAY(7.92893218813452,15,22.07106781186548,15,15,22.07106781186548))
  35. </pre></code>
  36. Now let's test and visualise some lines and circles.
  37. <code id="SourceCode"><pre>
  38. with line as (
  39. select sdo_geometry('LINESTRING(0 0, 10 10, 10 0, 20 10)',0) as line from dual
  40. )
  41. select SC4O.ST_MinimumBoundingCircle(line,2) as dGeom from line;
  42. .
  43. DGEOM
  44. -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  45. MDSYS.SDO_GEOMETRY(2003,NULL,MDSYS.SDO_POINT_TYPE(10,5,11.1803398874989),MDSYS.SDO_ELEM_INFO_ARRAY(1,1003,4),MDSYS.SDO_ORDINATE_ARRAY(-1.1803398874989,5,21.1803398874989,5,10,16.1803398874989))
  46. .
  47. -- Optimized Rectangle
  48. with rect as (
  49. select sdo_geometry(2003,null,null,sdo_elem_info_array(1,1003,3),sdo_ordinate_array(1,1,10,10)) as rect from dual
  50. )
  51. select SC4O.ST_MinimumBoundingCircle(rect,2) as dGeom from rect;
  52. .
  53. DGEOM
  54. ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  55. MDSYS.SDO_GEOMETRY(2003,NULL,MDSYS.SDO_POINT_TYPE(5.5,5.5,6.36396103067893),MDSYS.SDO_ELEM_INFO_ARRAY(1,1003,4),MDSYS.SDO_ORDINATE_ARRAY(-0.86396103067893,5.5,11.86396103067893,5.5,5.5,11.86396103067893))
Which look like: *1. Line* !http://www.spatialdbadvisor.com/images/134.png! *2. Rectangle* !http://www.spatialdbadvisor.com/images/135.png! I hope this helps someone.

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Comment [2]

What an interesting concept!

Now to find a use for it :)

— Thomas · 13 September 2011, 00:31 · #

Thomas,

Well, it is a part of JTS, and even has its own Wikipedia page, called Smallest circle problem so it must be useful!

I suspect its main area of application is in spatial statistics.

regards
Simon

Simon Greener · 13 September 2011, 06:12 · #