[postgis-users] out of memory when using simplify

[John Cole]

Hello,
  I'm trying to do some processing on a roads layer and simplify it for
rendering speed.  In ArcInfo, I would use a dissolve on the hwy_num field
and then simplify it to 500 meters.
 
  From the documentation, PostGIS seems like it can do the same thing, first
selecting into a new table using either the GeomUnion or Collect aggregates
and then again using simplify, however using simplify returns the following
error:
 
ERROR:  out of memory
DETAIL:  Failed on request of size 4172712.
 
here is my query:
    select hwy_num, simplify(the_geom, 500) as the_geom from ra1bb
 
where ra1bb is created from:
    select hwy_num, geomunion(the_geom) as the_geom into ra1bb from ra1
group by hwy_num
 
Another question:  what is the difference between collect and geomunion
(besides speed)?  Which one would better approximate an ArcInfo dissolve
function?
 
Thanks,
 
John Cole

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