[postgis-users] geomunion question, unexpected behavior

[rm_postgis at cheapcomplexdevices.com]

On Wed, 1 Dec 2004, Ethan Alpert wrote:
>
>
> I had a lot of these types of problems previously and I upgraded to
> 0.9.0 and GEOS 2.0 to correct the problem. I did narrow my problem down
> to GEOS having problems with Geometries that were the same. You may try
> selecting distinct geometries to pass to geomunion.


Hmm... I am using GEOS 2.0.1...


 fl=# select postgis_full_version();
                                          postgis_full_version
 -----------------------------------------------------------------------------------------------------
   POSTGIS="0.9.0" GEOS="2.0.1" PROJ="Rel. 4.4.8, 3 May 2004" USE_STATS DBPROC="0.0.1" RELPROC="0.0.1"
 (1 row)



> You may want to make sure all your geometries are valid. Do a select
> isvalid(the_geom)

Interesting.   If I read these statements right,'collect' of a set of
valid geometries seems to be returning an invalid geometry:

fl=# select isvalid(collect(distinct the_geom)) from user_area_features where featureid=18844;
 isvalid
---------
 f
(1 row)

fl=# select distinct isvalid(the_geom) from user_area_features where featureid=18844;
 isvalid
---------
 t
(1 row)



Thanks for the pointers.....   I'm still looking.