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.