That is a little odd. What are you using to view the data. I know for example QuantumGIS leaves out some geometries (particularly when they are large geometries) unless you change some setting on it. I noticed this once when I loaded up a large Candadian dataset and thinking - THATS CANADA. Then I changed some setting and all looked fine. With ST_Collect you probably get more geometries in your MULTIPOLYGON than ST_Union since it won't dissolve the boundaries, but you shouldn't be getting any geometries left out. Hope that helps, Regina
________________________________ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of danny Sent: Monday, August 04, 2008 8:24 AM To: PostGIS Users Discussion Subject: Re: [postgis-users] Merge all polygons from a dataset Thanks Regina. For some reason ST_Collect doesn't give exactly the same result. For example I'm trying to merge european countries in one shape and with ST_Collects it omits England and other islands while ST_Union includes them. Anyway, my union finished after 4 hours. I'm joining two tables on an ST_Intersect, one of which has ~15000 features (polygons) and the other just one (a complex polygon). The query's been running for two hours... I hope I'll see the end of it before the end of the day! (I've set the indexes where I could and tuned PostgreSQL) Regards. On Mon, Aug 4, 2008 at 12:25 PM, Obe, Regina <[EMAIL PROTECTED]> wrote: 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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] 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 <[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]> 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 [EMAIL PROTECTED] 804-698-4405 Open Source Modeling Tools: http://sourceforge.net/projects/npsource/ -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] 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 <[EMAIL PROTECTED]> 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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of danny Sent: Friday, August 01, 2008 6:12 AM To: [email protected] 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 ________________________________ The substance of this message, including any attachments, may be confidential, legally privileged and/or exempt from disclosure pursuant to Massachusetts law. It is intended solely for the addressee. 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