[postgis-users] Problem with slow GeomUnion (geom, geom)

[Matt Doughty]

Hi,

I managed to union the two tables through a simple union in the end:

CREATE TABLE newtable AS
	SELECT 
		Table1.name,
		Table1.the_geom
	FROM 	
		Table1
	UNION
	SELECT 
		Table2.name,
		Table2.the_geom
	FROM 
		Table2;

This didn't quite work as I wanted, as you can only set it to output the attributes of one of the tables, but serves its purpose for now. 

I don't think the Intersection(geometry,geometry) would've been relevant as this leaves only the geometries of the polygons where they overlap (or intersect).

Thanks for you inputs,

Matt 
 
Matt Doughty
 
GEOGRAMA S.L.
Tel.:  +34 945 13 13 72    652 77 14 15
Fax: +34 945 23 03 40 
www.geograma.com
 
 
-----Mensaje original-----
De: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-bounces at postgis.refractions.net] En nombre de Håvard Tveite
Enviado el: viernes, 01 de junio de 2007 16:17
Para: PostGIS Users Discussion
Asunto: Re: [postgis-users] Problem with slow GeomUnion (geom, geom)

This is probably a map overlay, and not a traditional spatial join.
See:

<URL: http://en.wikipedia.org/wiki/Geographic_information_system#Map_overlay >

The PostGIS Intersection(geometry,geometry) is a relevant
operation.

Håvard

Mark Cave-Ayland wrote:
> On Fri, 2007-06-01 at 12:00 +0200, Matt Doughty wrote:
>> Hi Mark,
>>
>> I'm trying to do a geometric union (I'm more used to doing these things
>> in ArcGIS where it'd be a union: A topological overlay of two or more
>> polygon spatial datasets that preserves the features that fall within
>> the spatial extent of either input dataset; that is, all features from
>> both datasets are retained and extracted into a new polygon dataset
>> (ESRI website))
>>
>> In this case I'm not bothered about what happens to attributes, it's the
>> polygons that I want.
>>
>> The input tables are as follows:
>>
>>       1. Table1
>>               name character varying(70),
>>               the_geom geometry
>>       2. Table 2
>>               name character varying(70),
>>               the_geom geometry
>> Cheers,
>>
>> Matt
> 
> Okay, this is getting a little out of my comfort zone so someone else
> may need to help out here - is basically what you want to return all the
> polygons that overlap each other from your two tables?
> 
> 
> Kind regards,
> 
> Mark.
> 
> --
> ILande - Open Source Consultancy
> http://www.ilande.co.uk
> 
> 
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-- 
Håvard Tveite
Department of Mathematical Sciences and Technology, UMB
Drøbakveien 31, POBox 5003, N-1432 Ås, NORWAY
Phone: +47 64965483 Fax: +47 64965401 http://www.umb.no/imt/
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