[postgis-users] geomunion revisited....

[Lee Keel]

> -----Original Message-----
> From: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-
> bounces at postgis.refractions.net] On Behalf Of Martin Davis
> Sent: Tuesday, November 13, 2007 10:28 AM
> To: PostGIS Users Discussion
> Subject: Re: [postgis-users] geomunion revisited....
> 
> buffer may or may not be faster than geomunion.  For "small" cases it
> almost certainly is.  However, for very large inputs it may bog down,
> because it loads and processes all geometries at once (and thus doesn't
> have a chance to eliminate linework which would be eliminated in the
> resulting union).  Geomunion, while inefficient as Kevin points out, at
> least has the chance to simplify the result geometry as it goes along.
> *However*, geomunion is "dumb" in that it doesn't try to union adjacent
> polygons first - so it doesn't simplify anywhere nearly as much as it
> could.
> 
> A better tool would be to use the new cascaded union operation in JTS
> (which hopefully can get ported to GEOS & PostGIS soon).
> 
> @Lee: are you positive about your ArcGIS result?  It's using exactly the
> same dataset?
> 
[Lee Keel] 

I am not sure how much the 'cascaded union' will help until it gets ported
to PostGIS.

As for the ArcGIS results, well....  I am as certain as I can be base on my
client.  I have not actually performed this operation for them, but
according to my contact there those are accurate numbers for the same
dataset.

-Lee
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