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:[EMAIL PROTECTED]
http://www.agi.so.ch <http://www.agi.so.ch/>
-----Ursprüngliche Nachricht-----
*Von:* Obe, Regina [mailto:[EMAIL PROTECTED]
*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:* [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] *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:[EMAIL PROTECTED]
http://www.agi.so.ch
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