[postgis-users] Merge all polygons from a dataset

[Obe, Regina]

Try the trick documented here
 
http://postgis.refractions.net/documentation/manual-svn/ST_Collect.html
 
On hindsight - I realized the ST_Multi call here is probably unnecessary
so you can leave that part out.
 
Hope that helps,
Regina
 
 

________________________________

From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of
danny
Sent: Monday, August 04, 2008 5:04 AM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] Merge all polygons from a dataset


I'm getting very long processing time from ST_Union (on a shape of
europe at 1/100000 it's been running since 2 hours and hasn't finished
yet; on my previous one of 1/1000000 it took ~1 hour)
Any other alternative and quicker ways to accomplish the same operation?
I just executed st_buffer(st_collect(the_geom)) but still waiting.
Should it take as long? ST_Collect by itself executes fast but it's
result violates the geometry check constraint. 




On Fri, Aug 1, 2008 at 5:31 PM, danny <whatevar89 at gmail.com> wrote:


	Thanks Robert.
	
	I actually exported from ogr2ogr and it created a shape that
worked fine in ArcView.
	
	Best 

	 
	
	
	
	On Fri, Aug 1, 2008 at 5:19 PM, Burgholzer,Robert
<rwburgholzer at deq.virginia.gov> wrote:
	

		Could ArcView perhaps want some columns other than just
the shape?  Perhaps you could put a numeric ID or something else in
there.

		 

		Just a thought,

		 

		Robert W. Burgholzer

		Surface Water Modeler

		Office of Water Supply and Planning

		Virginia Department of Environmental Quality

		rwburgholzer at deq.virginia.gov

		804-698-4405

		Open Source Modeling Tools:

		http://sourceforge.net/projects/npsource/

		
		-----Original Message-----
		From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of
danny
		
		Sent: Friday, August 01, 2008 9:30 AM
		To: PostGIS Users Discussion
		Subject: Re: [postgis-users] Merge all polygons from a
dataset

		

		 

		Many thanks, Regina! Indeed ST_Union generated the
polygon, invisible in PgAdmin!! 
		
		It creates a nice layer when I open it in uDig. 
		
		However when I export it with pgsql2shp, the shape is
unreadable by ArcView with the errmsg: Number of shapes does not match
the number of table records.
		
		Here's how I created the layer:
		
		create table europe_contour();
		SELECT addgeometrycolumn('db, 'europe_contour',
'the_geom', 32767,'MULTIPOLYGON', 2 );
		insert into europe_contour(the_geom) values( (select
st_union(the_geom) from europe));
		
		Then I generate the shapefile: 
		
		"c:\Program Files\PostgreSQL\8.3\bin\pgsql2shp.exe" -u
postgres -P password -f europe_contour db europe_contour
		
		Any suggestions perhaps on anything I've wrong?
		
		

		On Fri, Aug 1, 2008 at 1:15 PM, Obe, Regina
<robe.dnd at cityofboston.gov> wrote:

		Erik,

		How were you using ST_Union and what exactly do you mean
by no result.  no result as it looks blank?  If you are using something
like PgAdmin III - it will look blank because it exceeds the buffer
supported by PgAdmin III.

		 

		SELECT the_geom is null 

		FROM (somequery or table) as foo

		LIMIT 1

		 

		will tell you if its actually returning no geometry

		 

		Hope that helps,

		Regina

		 

		
________________________________


		From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of
danny
		Sent: Friday, August 01, 2008 6:12 AM
		To: postgis-users at postgis.refractions.net
		Subject: [postgis-users] Merge all polygons from a
dataset

		Hello everybody,
		
		I've converted a shapefile of Europe to PostGIS. I would
like to merge all the countries together so that I only have one polygon
left, the whole contour of Europe. I have tried ST_Union that gives me
no result. I've tried several other functions to no avail. Does anybody
know how I should proceed?
		
		Many thanks,
		
		Erik

		
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