[postgis-users] [?? Probable Spam] Re: multipolygon to single polygon

Thu Apr 26 09:02:59 PDT 2012

you can alss use a "with" statement as indicated by nicolas, but be 
certain that what you want is to get the "sum" of all polygon of your 
collection

bye

Le 26/04/2012 17:51, ju a écrit :
> ok so this is second solution.
>
> 1) fisrt count the number of objet of the collection
>
> select ST_NumGeometries(the_geom) as the_nb from YOURTABLE
>
> you will obtain the number of collection, so probably 4 polygon
>
> 2) then "explose" theses 4 polygon :
>
> SELECT
> what you want....,
> n,
> ST_GeometryN(the_geom, n) as geom_unique,
> ST_astext(ST_GeometryN(the_geom, n)) as geom_unique_txt
> FROM YOURTABLE CROSS JOIN generate_series(1,100) n
> WHERE n <= ST_NumGeometries(the_geom);
>
> note : 100 is default for serie, if you count 4 objet in collection 
> you can write serie(1,4)
>
> you shoud obtain 4 rows, the text format is juste here so as you see 
> the polygon coordinate
>
>
> 3) 2 choices
>
> 3.1 if one of the 4 polygon is what you want, then use it. for example 
> if it is the n number 3 then update your table with
>
> update YOURTABLE set the_geom =
> ST_GeometryN(the_geom, 3)
> (dont forget a WHERE .... id of the row you want to update)
>
> 3.2) if you want to group all the 4 polygone to make a new one there 
> are other possibility
> - for example make a table  with the 4 polygons ( same query but 
> "select into table" .....)
> with this table make a dissolve query to group the 4 objetc
> - update your table with the result of dissolve
>
> - you can also use array to group, etc...
>
>
> tip : sometimes it is quick to copy /past result wkt of query
> for example you copy the result wkt of the  query  for objet 
> collection number 3:
>
> POLYGON((892426.5625 6463663,892432.9375 6463678,892434.4375 
> 6463685,892454.75 6463802,892457.0625 6463879.5,892456.6875 
> 6463879.5,892453.6875 6463931,892453 6463931))
>
> then  you make a polygon with it :
>
> update matable set the_geom = ST_GeometryFromText('POLYGON((892426.5625 6463663,892432.9375 6463678,892434.4375
> 6463685,892454.75 6463802,892457.0625 6463879.5,892456.6875
> 6463879.5,892453.6875 6463931,892453 6463931))'
> (dont forget a WHERE .... id of the row you want to update)
>
>
> Le 26/04/2012 17:22, Mehmet Erkek a écrit :
>>
>> Hi Juilen, thanks for quick answer.
>>
>> I have 1 geometry and 1 row on the table. this geometry is 
>> multiploygon which consists of 4 polygons.
>>
>> I want to convert this mutlipolygon to one single polygon..
>>
>> Any idea how I can do this?
>>
>> I hope it is clearer now.
>>
>> Thanks.
>>
>> *From:*postgis-users-bounces at postgis.refractions.net 
>> [mailto:postgis-users-bounces at postgis.refractions.net] *On Behalf Of *ju
>> *Sent:* 26 Nisan 2012 18:02
>> *To:* PostGIS Users Discussion
>> *Subject:* Re: [postgis-users] [!! SPAM] multipolygon to single polygon
>>
>> not clear...
>>
>> 1) if you have 4 polygons in 4 rows table distinct, this is not a 
>> multi object issu. for  this case use
>>  dissolve to group polygone into only one, this is not a topic of dump.
>>
>>
>> 2) if you have 1 geometry and 1 row on the tablme, so this is a multi 
>> object topic
>> you must sperate the differents objet of the collection
>>
>> here : http://www.postgis.org/docs/ST_GeometryN.html
>>
>> --Extracting all geometries (useful when you want to assign an id)
>> SELECT gid, n, ST_GeometryN(the_geom, n)
>> FROM sometable CROSS JOIN generate_series(1,100) n
>> WHERE n<= ST_NumGeometries(the_geom);
>>
>>
>> best regards, julien
>>
>>
>>
>> Le 26/04/2012 16:27, Mehmet Erkek a écrit :
>>
>> I have multipolygons which I would like to convert a single polygon. 
>> is there a way to do this? please check the attached image. I tried 
>> st_dump and afterwards st_union , but eventually I get a multipolygon 
>> again, not polygon.
>>
>> *Mehmet Erkek*
>>
>> www.REIDIN.com <http://www.reidin.com/>
>>
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> Parc National des Ecrins
> Domaine de Charance
> 05 000 GAP
> tél : 04.92.40.20.10
> fax : 04.92.52.38.34
> julien.guilloux at ecrins-parcnational.fr
>
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Parc National des Ecrins
Domaine de Charance
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fax : 04.92.52.38.34
julien.guilloux at ecrins-parcnational.fr

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