Using SDO_GEOM.VALIDATE_GEOMETRY_WITH_CONTEXT effectively

Question

I have been using SDO_GEOM.VALIDATE_GEOMETRY_WITH_CONTEXT to validate the geometry of several million polygon features. Here is an example of the SQL I have been using:
Create table myResultsTable
as
SELECT A.myID, SDO_GEOM.VALIDATE_GEOMETRY_WITH_CONTEXT(A.GEOMETRY, 0.1) as invalidGeometry, FROM myGeometryTable A
WHERE SDO_GEOM.VALIDATE_GEOMETRY_WITH_CONTEXT(A.GEOMETRY, 0.1) <> 'TRUE';
I noticed that for each polygon in the table, this function returns only one result for the polygon before moving on to the next polygon despite it being possible that a polygon could fail the validation for several reasons.
How can I return all reasons why a polygon has invalid geometry?
Does it require me to use PL/SQL? If so, can anyone get me started?
Or does it require me to use SDO_GEOM.VALIDATE_LAYER_WITH_CONTEXT? If so, how do I specify a tolerance when using this function like I did when I used SDO_GEOM.VALIDATE_GEOMETRY_WITH_CONTEXT?
Many thanks for your time.

Answer 1

Hi,
The validation routines only report the first reason geometry data is invalid.
To validate several million polygon features I would use validate_layer_with_context because it is faster.
If you don't want to for some reason then alter your statement to only run the validation procedure once:
select a.status,a.id
from (SELECT m.myID id, SDO_GEOM.VALIDATE_GEOMETRY_WITH_CONTEXT(m.GEOMETRY, 0.1) status
FROM myGeometryTable m) a
where a.status <> 'TRUE';
Then there are possibilities in terms of automatically trying to fix things up to move on to the next error. For instance, if you get a duplicate vertices error your run remove_duplicate_vertices to try to fix that error, then revalidate and see if there are other errors. If you have a self-intersecting geometrt then running a self union may fix those kinds of problems (in 10g r2 this is automated with sdo_util.rectify_geometry, which attempts to automatically fix these kinds of errors).
NOTE: Always check results of any automated geometry fix-up procedures to make sure you agree with the results of the procedure. I would recommend against automatically updating your data without checking the results.
Hope this helps,
Dan