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

[Düster Horst]

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 

 

   -----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


   
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