[postgis-users] Invalid geometry? (and side location conflict)

[Rob Tester]

I receive an error when getting the area for an intersection of two geometry objects. One is large containing several hundered points the other was much smaller. 

I get:

NOTICE:  TopologyException: side location conflict (-84.4858,33.6872,33.6872)

ERROR:  GEOS Intersection() threw an error!

(note that geomunion with the same geometry objects works fine)

After reading the email lists I saw that invalid geometry objects are often the cause this error, so I checked them with isValid(). Sure enough the large geometry returns false. My question is what really makes a geometry invalid? Is it the invalid geometry that is really causing this issue or something related to the intersection (since geomunion works fine)?

I have tried the intersection with other polygons and have had no problems, but one table that contains these very large polygons always causes this problem.

Any help is greatly appreciated.

Thanks

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