CENTROID Package now returns centroid of multi-linestring
My original CENTROID package’s sdo_centroid() functions, when supplied with a multilinestring sdo_geometry, would “explode” the multilinestring into its component linestrings and calculate the centroid (mid-point) of the largest linestring.
Some users have asked for the centroid package to return the centroid (midpoint) of the whole multilinestring. While the LINEAR package can do this, I have modified the CENTROID package so that it can return either via an option called p_line_explode.
If p_line_explode is set to 1 then the sdo_centroid() function will operate as it always has, but if set to 0, then the midpoint (at half-length) of the entire multipoint is returned.
/* ---------------------------------------------------------------------------------------- * @function : SDO_Centroid * @precis : Generates centroid for a polygon. * @version : 1.0 * @description: The standard MDSYS.SDO_GEOM.SDO_GEOMETRY function does not guarantee * that the centroid it generates falls inside the polygon. Nor does it * generate a centroid for a multi-part polygon shape. * This function ensures that the centroid of any arbitrary polygon * falls within the polygon. * @usage : Function Do_Centroid( * p_geometry IN MDSYS.SDO_GEOMETRY, * p_dimarray IN MDSYS.SDO_DIM_ARRAY, * p_area IN NUMBER, * p_line_explode IN NUMBER) * RETURN MDSYS.SDO_GEOMETRY DETERMINISTIC; * @param : p_geometry : MDSYS.SDO_GEOMETRY : The geometry object. * @param : p_tolerance : Number : Tolerance used when processing vertices. * Expressed in dataset units eg decimal degrees if 8311. * See Convert_Distance for method of converting distance in meters to dataset units. * @param : p_area : Number : Whether largest part in a multi-part polygon should be chosen as part with largest * area (1) or with largest MBR (not 1) * @param : p_line_explode : Number : Whether largest part in a multi-linestring should be used for centroid or chose * centroid based on 50% of length across all parts. * @return : centroid : MDSYS.SDO_GEOMETRY : The centroid. * @requires : GetVector() * @requires : tolerance * @note : Does not check if passed shape is a polygon. * @history : Simon Greener - Mar 2008 - Total re-write of algorithm following on from cases the original algorithm didn't handle. * The new algorithm does everything in a single SQL statement which can be run outside of this function if needed. * The algorithm is based on a known method for filling a polygon which counts the type and number of crossings of a * "ray" (in this case a vertical line) across a polygon boundary. The new algorithm also has improved handling of * multi-part geometries and also generates a starting X ordinate for the vertical "ray" using vertex averaging * rather than the mid point of a part's MBR. This is to try and "weight" the centroid more towards where detail exists. * Simon Greener - Jul 2008 - Standalone version with no dependencies other than the need for external object types. * @copyright : Free for public use **/ FUNCTION sdo_centroid ( p_geometry IN MDSYS.SDO_Geometry, p_tolerance IN NUMBER, p_area IN NUMBER := 1, p_line_explode IN NUMBER := 1) RETURN MDSYS.SDO_Geometry deterministic; /** * Overload of main sdo_centroid function **/ FUNCTION Do_Centroid( p_geometry IN MDSYS.SDO_GEOMETRY, p_dimarray IN MDSYS.SDO_DIM_ARRAY, p_area IN NUMBER := 1, p_line_explode IN NUMBER := 1) RETURN MDSYS.SDO_Geometry deterministic;
Example
SELECT CODESYS.centroid.sdo_centroid(MDSYS.SDO_GEOMETRY(2006, NULL, NULL, MDSYS.SDO_ELEM_INFO_ARRAY(1,2,1,5,2,1), MDSYS.SDO_ORDINATE_ARRAY(50.0, 15.0, 55.0, 15.0, 60.0, 15.0, 65.0, 15.0)),0.005,1,1) AS mcentroid, CODESYS.centroid.sdo_centroid(MDSYS.SDO_GEOMETRY(2006, NULL, NULL, MDSYS.SDO_ELEM_INFO_ARRAY(1,2,1,5,2,1), MDSYS.SDO_ORDINATE_ARRAY(50.0, 15.0, 55.0, 15.0, 60.0, 15.0, 65.0, 15.0)),0.005,1,0) AS centroid FROM dual; MCENTROID CENTROID -------------------------------------------------------------------------- ------------------------------------------------------------------------ MDSYS.SDO_GEOMETRY(2001,NULL,MDSYS.SDO_POINT_TYPE(52.5,15,NULL),NULL,NULL) MDSYS.SDO_GEOMETRY(2001,NULL,MDSYS.SDO_POINT_TYPE(55,15,NULL),NULL,NULL)
Visually
I hope this is of help to someone.