[postgis-users] Array Size Error

[Paragon Corporation]

Paul,

 

I think Leo had something in mind like this:

 

WITH ctsubgroup AS 

    ( SELECT ST_ConvexHull(ST_Force_2D(ST_Union(geom))) As geom

    FROM table001

    GROUP BY ST_SnapToGrid(geom, 10,10)

)

SELECT ST_ConvexHull(ST_Union(geom))

FROM ctsubgroup;

 

The 10,10 should be dependent on your spatial ref , you can make larger
groupings the bigger you make that grid snap.

The idea is you want your subsets to be smaller than max size of array
allowed.

 

http://www.postgis.org/documentation/manual-svn/ST_SnapToGrid.html

 

 

In theory I think ST_MemCollect may work, but will take a really really long
time for that many points 

and once it's done collecting, it would push the whole thing to PostGIS/GEOS
to collapse, which will probably lead to other limit issues.

 

Hope that helps,

Regina

http://www.postgis.us <http://www.postgis.us/> 

 

 

  _____  

From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Paragon
Corporation
Sent: Wednesday, July 27, 2011 6:38 AM
To: 'PostGIS Users Discussion'
Subject: Re: [postgis-users] Array Size Error

 

Paul,

 

I think it's a waste of time.  Your best bet is to collect your geometries
into groups an do a convex hull of each group and then the convexhull of the
convexhulls

 

 

Leo

http://www.postgis.us <http://www.postgis.us/> 

 

  _____  

From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Paul &
Caroline Lewis
Sent: Wednesday, July 27, 2011 5:32 AM
To: PostGIS Users
Subject: [postgis-users] Array Size Error

 

Thanks for the responses. Have changed the original query from this:
 
SELECT ST_ConvexHull(ST_Collect(ST_Force_2D(geom))) FROM table001
 
to this:
 
SELECT ST_ConvexHull(ST_MemUnion(geom)) FROM table001
 
and its still running; over 12 hours now.
Is this a waste of time.
I'm trying it this way as I guessed it could be an aggregate approach issue
after reading this post from Paul:
 
http://blog.cleverelephant.ca/2009/01/must-faster-unions-in-postgis-14.html
 
and was wondering if the union operation might work for my current
requirements so set it running yesterday. 
The ST_Union gives the same array size error after a few seconds but as I
said the ST_MemUnion is still running, but is it working or going to work!!!
 
Anyway, thanks again for your feedback.
 
Paul

 

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