AW: RE: [postgis-users] Geometrycollection to Multipolygon

[Stephen Woodbridge]

I think you are getting the collection because you are mixing types.
Try this (I haven't tried it):

st_collect(
   st_collect(st_multi(polygon1), st_multi(polygon2)),
   st_multi(polygon3))

and see if you get a multipolygon ot a collection as the result.

-Steve W

Düster Horst wrote:
> 
> Regina
>  
> Thank you for your response. Mmmm.. your trick doesn't solve my problem. 
> Perhaps I should tell you why I do have a geometrycollection. My 
> startingpoint is a sequence of single polygons. My aim is to merge them 
> together to one multipolygon. I do this with st_collect. This works fine 
> with two polygons:
>  
> st_collect(polygon1,polygon2) => multipolygon(1,2).
>  
> When I Process the third polygon with: st_collect(multipolygon(1,2), 
> polygon3)  => Geometrycollection(multipolygon(1,2),polygon3)
>  
> I do get the geomtrycollection and so on.
>  
> My main problem is to merge the three polygons into one multipolygon 
> with 3 geometries.
>  
> When I solve this problem I can offer a procedure to clean invalid 
> geometries.
>  
> Regards
> Horst
>  
> 
> ------------------------------------------------
> 
> Dr. Horst Düster
> GIS-Koordinator, Stv. Amtschef
> 
> Kanton Solothurn
> Bau- und Justizdepartement
> Amt für Geoinformation
> SO!GIS Koordination
> Rötistrasse 4
> CH-4501 Solothurn
> 
> Telefon ++41(0)32 627 25 32
> Telefax ++41(0)32 627 22 14
> 
> mailto:horst.duester at bd.so.ch
> http://www.agi.so.ch <http://www.agi.so.ch/>
> 
>  
> 
>     -----Ursprüngliche Nachricht-----
>     *Von:* Obe, Regina [mailto:robe.dnd at cityofboston.gov]
>     *Gesendet am:* Mittwoch, 23. April 2008 14:24
>     *An:* PostGIS Users Discussion
>     *Betreff:* RE: [postgis-users] Geometrycollection to Multipolygon
> 
>     This sometimes does the trick for me if they actually can be unioned
>      
>      ST_Union(GEOMCOLL, ST_GeomFromText('GEOMETRYCOLLECTION(EMPTY)',
>     yoursridhere) )
>      
>     (your number 2 doesn't work because that is the aggregate form, not
>     because ST_Union can't handle geometry collections I think)
>      
>      
>     Hope that helps,
>     Regina
>        *From:* postgis-users-bounces at postgis.refractions.net
>     [mailto:postgis-users-bounces at postgis.refractions.net] *On Behalf Of
>     *Düster Horst
>     *Sent:* Wednesday, April 23, 2008 2:25 AM
>     *To:* postgis-users
>     *Subject:* [postgis-users] Geometrycollection to Multipolygon
> 
>     I do have a Geometrycollection which consists of a collection of
>     Multipolygons and Polygons. My aim is to create one single
>     Multipolygon from the mentioned Geometry collection.
> 
>     Until now I tried the following steps without result:
> 
>     1. ST_BUFFER(GEOMCOLL,0.0) => It works but all inner rings of my
>     input geometry are lost.
>     2. ST_UNION(GEOMCOLL) => doesn't work with Geometrycollections
> 
>     Does anyone has a solution to solve my problem?
> 
>     Best regards
>     Horst
> 
>     ------------------------------------------------
> 
>     Dr. Horst Düster
>     GIS-Koordinator, Stv. Amtschef
> 
>     Kanton Solothurn
>     Bau- und Justizdepartement
>     Amt für Geoinformation
>     SO!GIS Koordination
>     Rötistrasse 4
>     CH-4501 Solothurn
> 
>     Telefon ++41(0)32 627 25 32
>     Telefax ++41(0)32 627 22 14
> 
>     mailto:horst.duester at bd.so.ch
>     http://www.agi.so.ch
> 
>       
> 
>     *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. If you received this in error, please contact the sender
>     and delete the material from any computer. *
> 
>       
> 
>     * Help make the earth a greener place. If at all possible resist
>     printing this email and join us in saving paper. *
> 
>     * *
> 
> 
> ------------------------------------------------------------------------
> 
> _______________________________________________
> postgis-users mailing list
> postgis-users at postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users