Top 5 Recent Articles

ARTICLES CATEGORIES

Free Union, Intersection, Xor and Difference Functions for Oracle Locator – Part 2

In this blog we will execute the four overlay types on two simple rectangular polygons.

In addition, I have not tested “real world” polygon data using multiple projections. I am just showing what is possible.

Here is the SQL that I use to create two test polygon geometries.

 SELECT 'GEOM1' AS gtype,
        sdo_geometry(2003,82469,NULL,sdo_elem_info_array(1,1003,3),sdo_ordinate_array(1,1,10,10)) AS geom
   FROM dual
 UNION ALL
 SELECT 'GEOM2' AS gtype,
        sdo_geometry(2003,82469,NULL,sdo_elem_info_array(1,1003,3),sdo_ordinate_array(5,5,15,15)) AS geom
   FROM dual

Here are what they look like.

Here is the SQL that I used to combine the above test polygon geometries.

 SELECT 'UNION' AS gtype,
        SC4O.ST_Union(sdo_geometry(2003,82469,NULL,sdo_elem_info_array(1,1003,3),sdo_ordinate_array(1,1,10,10)),
                      sdo_geometry(2003,82469,NULL,sdo_elem_info_array(1,1003,3),sdo_ordinate_array(5,5,15,15)),
                      1) AS rGeom
   FROM dual
 UNION ALL
 SELECT 'INTERSECTION' AS gtype,
        SC4O.ST_Intersection(sdo_geometry(2003,82469,NULL,sdo_elem_info_array(1,1003,3),sdo_ordinate_array(1,1,10,10)),
                             sdo_geometry(2003,82469,NULL,sdo_elem_info_array(1,1003,3),sdo_ordinate_array(5,5,15,15)),
                             1) AS rGeom
   FROM dual
 UNION ALL
 SELECT 'XOR' AS gtype,
        SC4O.ST_XOr(sdo_geometry(2003,82469,NULL,sdo_elem_info_array(1,1003,3),sdo_ordinate_array(1,1,10,10)),
                    sdo_geometry(2003,82469,NULL,sdo_elem_info_array(1,1003,3),sdo_ordinate_array(5,5,15,15)),
                    1) AS rGeom
   FROM dual
 UNION ALL
 SELECT 'DIFFERENCE' AS gtype,
        SC4O.ST_Difference(sdo_geometry(2003,82469,NULL,sdo_elem_info_array(1,1003,3),sdo_ordinate_array(1,1,10,10)),
                           sdo_geometry(2003,82469,NULL,sdo_elem_info_array(1,1003,3),sdo_ordinate_array(5,5,15,15)),
                           1) AS rGeom
   FROM dual;

The following image shows the result of executing four Overlay types on two simple rectangular polygons visually using GeoRaptor’s neat Thumbnail capability.

NOTE 1: JTS doesn’t currently support geodetic computations. If you wish to use this package with geodetic data then you should:

  • Transform (sdo_cs.transform) your data to a suitable projected coordinate system, eg UTM;
  • Call the relevant JTS function;
  • Transform the result back to you original geodetic SRID.