[geos-devel] TopologyException: found non-noded intersection

[G. Allegri]

I'm using Postgis 1.5.1 to compute a Union on a quite large
multipolygons dataset (some hundreds of thousands of features), but
I'm facing the following error:

NOTICE:  TopologyException: found non-noded intersection between
LINESTRING (1.7318e+006 4.77959e+006, 1.7318e+006 4.77958e+006) and
LINESTRING (1.7318e+006 4.77958e+006, 1.73174e+006 4.77954e+006) at
1.7318e+006 4.77958e+006

ERROR:  GEOS union() threw an error!

I know it's a known issue, but I haven't been able to find a good,
replicable, solution. The input geometries result valid (in simple
feature meaning).
What is causing this? I have overlapping polygons, but I thought the
cascaded union algorithm computed the necessary noding on the
linestrings.
I've supposed it depends on tolerances/precision model, but I don't if
it makes sense and how, eventually, tune it.

Thanks a lot,
Giovanni