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# Free Union, Intersection, Xor and Difference Functions for Oracle Locator – Part 4 Processing Geodetic data

As I have indicated in this series, the Java Topology Suite (JTS) collection of algorithms on which this implementation is based, currently does not support geodetic computations.

Simply put, ** if your data is longitude/latitude then the results of any computations will be inaccurate**.

If you wish this package to work geodetic data and produce correct results then you should:

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

Worked examples of this will now be provided:

select SDO_GEOMETRY(2003,8265,NULL,SDO_ELEM_INFO_ARRAY(1,1003,1),SDO_ORDINATE_ARRAY(-79.230998,35.837119,-79.230480,35.836701,-79.230386,35.836838,-79.230884,35.837222,-79.230998,35.837119)) as g1, SDO_GEOMETRY(2003,8265,NULL,SDO_ELEM_INFO_ARRAY(1,1003,1),SDO_ORDINATE_ARRAY(-79.230974,35.836828,-79.230802,35.836720,-79.230454,35.837183,-79.230664,35.837300,-79.230974,35.836828)) as g2 from dual;

-- What is SRID 8265? select cs_name from cs_srs where srid = 8265; CS_NAME ----------------------------- Longitude / Latitude (NAD 83) -- What is a suitable UTM zone to use when processing this SRID's data? -- select srid, central_meridian from (select srid, cs_name, to_number(replace(t.column_Value,'"Central_Meridian", ',null),'S999.000000') as central_meridian from cs_srs c, table(geom.tokenizer(c.wktext,'[]'))t where cs_name like 'UTM%NAD 83%' and t.column_value like '"Central_Meridian%' ) cm, (select centroid.sdo_centroid(SDO_GEOMETRY(2003,8265,NULL,SDO_ELEM_INFO_ARRAY(1,1003,1),SDO_ORDINATE_ARRAY(-79.230998,35.837119,-79.230480,35.836701,-79.230386,35.836838,-79.230884,35.837222,-79.230998,35.837119)),0.0000001) as point from geodpoly2d p) p where p.point.sdo_point.x between cm.central_meridian - 3 and cm.central_meridian + 3 ; SRID CENTRAL_MERIDIAN ----- ---------------- 82247 -81 -- Now execute a union (correctly) With twoPolys As ( select SDO_GEOMETRY(2003,8265,NULL,SDO_ELEM_INFO_ARRAY(1,1003,1),SDO_ORDINATE_ARRAY(-79.230998,35.837119,-79.230480,35.836701,-79.230386,35.836838,-79.230884,35.837222,-79.230998,35.837119)) as g1, SDO_GEOMETRY(2003,8265,NULL,SDO_ELEM_INFO_ARRAY(1,1003,1),SDO_ORDINATE_ARRAY(-79.230974,35.836828,-79.230802,35.836720,-79.230454,35.837183,-79.230664,35.837300,-79.230974,35.836828)) as g2 from dual ) select sdo_cs.transform(pinter,8265) as geom8265 from (select geoprocess.intersection( sdo_cs.transform(g1,82247), sdo_cs.transform(g2,82247),6) pinter from twoPolys );

**Buffering is less complicated**

select sdo_cs.transform(geoprocess.buffer(sdo_cs.transform(g1,82247),10,2),8265) as buffGeom from (select SDO_GEOMETRY(2003,8265,NULL,SDO_ELEM_INFO_ARRAY(1,1003,1),SDO_ORDINATE_ARRAY(-79.230998,35.837119,-79.230480,35.836701,-79.230386,35.836838,-79.230884,35.837222,-79.230998,35.837119)) as g1 from dual );

Finally, sdo_cs.transform() comes with a heavy setup cost. This is OK if you are only processing a single geometry or two but if you are processing a lot, such as buffering a whole table of geometry data, then those costs will create a significant performance penalty. When bulk processing data it is better to use sdo_cs.transform_layer() as the setup costs are incurred once, with the transformation parameters reused for each and every geometry processed.

## Documentation

- MySQL Spatial General Function Documentation
- Oracle Spatial Exporter Package Documentation
- Oracle Spatial Object Function Documentation
- Oracle Spatial Object Function Documentation (Multi Page Version)
- PostGIS pl/pgSQL Function Documentation
- SC4O Oracle Java Topology Suite (Stored Procedures) Package Documentation
- SQL Server Spatial General TSQL Function Documentation
- SQL Server Spatial LRS TSQL Function Documentation