[postgis-users] Postgis errors

[Brent Wood]

Can anyone offer some advice?

The source data was downloded from a NOAA site, as topologically correct e00
files. If an upgrade for PostGIS/GEOS is likely to help I'll try to get the IT
staff to do this.



I have a "layer" which is giving me problems when queried with PostGIS.
The layer is derived from a table of MULTIPOLYGONS, each record being
datestamped and having a density value (ct).

I'm trying to derive the outer boundary for selected polygons at particular
dates, for specified density ranges. The SQL (embedded in a script to loop
through the required dates) is:

CT2a=1
CT2b=35
psql $DB -t -A -c "select $CT2a as new_ct,
               transform(boundary(memgeomunion(simplify(the_geom,300))), 4326)
                       from natice
                       where _date = '$DATE'
                         and ct >= $CT2a
                         and ct <= $CT2b
                       group by new_ct;" >> ${DATE}.txt

I get occasional different errors, depending on whether & how much I simplify
the source data & memgeomunion seems more robust than geomunion.

with:
transform(boundary(memgeomunion(the_geom)),4326)

retrieving category 4 CT boundary (>41)
  (68 polygons to merge)
NOTICE:  TopologyException: side location conflict (-789350,2.03517e+06)
ERROR:  GEOS union() threw an error!

but change the query to:
transform(boundary(memgeomunion(simplify(the_geom,600))),4326)
and it works perfectly.

Another PostGIS error which is simplify dependent (changing simplify can
prevent the error) is:
retrieving category 3 CT boundary (30 - 40)
   (3 polygons to merge)
NOTICE:  TopologyException: no outgoing dirEdge found
(-1.40494e+06,2.56829e+06)
ERROR:  GEOS union() threw an error!


software versions installed:

PostgreSQL 7.4.2,             

postgis_version
---------------------------------------
 0.8 USE_GEOS=1 USE_PROJ=1 USE_STATS=1

and I think geos-1.0-2



Any help appreciated.

  Brent Wood