[postgis-users] Still can't make sense of this error

[Mark Fenbers]

OK, now that we got the source of the message garbage out ot the way, I 
need to restate my unresolved problem...

I'm consistently getting an error that I cannot make sense of.  Here's 
the query I run:

SELECT 'ILN' AS "base radar",radid,
    AsText(
            Difference(
                base_geom,
                x_geom
            )
    )
    FROM MJF WHERE radid != 'ILN'
     AND IsValid(x_geom) AND IsValid(base_geom);

Here's the error I get::

NOTICE:  TopologyException: no outgoing dirEdge found (34380.5,521104)
ERROR:  GEOS difference() threw an error!

If I change my query such that only one row is returned (such as adding 
"LIMIT 1", or changing the WHERE clause from "!=" to "="), then I do NOT 
get the error.   I get the error whether I use Difference(), 
Intersection(), GeomUnion(), or the like, whenever more than one row is 
returned.   The 'base_geom' contains a circular geometry returned from 
the Buffer() function (to create a disk around point).  The x_geom is a 
rectangle that I know intersects the circle (base_geom).  Any ideas how 
to interpret this error or get around it?

Mark

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