[postgis-users] MULTILINESTRING to MULTIPOLYGON

[Birgit Laggner]

Hi Javier,

you could add the missing end point (and then try again with 
ST_BuildArea() etc.). Here a more or less suiting example of the PostGIS 
manual for ST_AddPoint():

UPDATE sometable
SET the_geom = ST_AddPoint(the_geom, ST_StartPoint(the_geom))
FROM sometable
WHERE ST_IsClosed(the_geom) = false;


With a MultiLineString, this might be a bit more complicated because you 
have to find out first, is your multilinestring resulting in a polygon 
or a multipolygon? If all linestrings form one polygon, you have to 
select the start point of the first linestring as end point of the last 
linestring. If the result is a multipolygon, you have to find out which 
of the rings is not closed, first. As I see from your first e-mail, you 
are expecting the geometry to become a multipolygon, so (assuming every 
linestring is representing a polygon within the multipolygon, otherwise 
it might be a solution to union the linestrings first) maybe the sql 
code could look like this:

UPDATE sometable a
SET the_geom = sel.geom FROM
(SELECT b1.gid, ST_Collect(b1.geom) AS geom --put together all linestrings to one multilinestring again
FROM
(SELECT b.gid, ST_AddPoint(b.geom, ST_StartPoint(b.geom)) --add an end point on the position of the start point for each non-closed linestring
FROM
(SELECT gid, (st_dump(the_geom)).geom AS geom --separate the linestrings and select the not closed ones
FROM sometable
WHERE ST_IsClosed(the_geom)=false) b
WHERE ST_IsClosed(b.geom) = false
UNION ALL
SELECT b.gid, b.geom
FROM
(SELECT gid, (st_dump(the_geom)).geom AS geom --separate the linestrings and select the closed ones
FROM sometable
WHERE ST_IsClosed(the_geom)=false) b
WHERE ST_IsClosed(b.geom) = true) b1
GROUP BY b1.gid) sel
WHERE ST_IsClosed(a.the_geom)=false AND a.gid=sel.gid;

I did not test the code, but I hope you get the idea...

Regards,

Birgit.


On 28.03.2011 18:47, Javier Perez wrote:
> Hi,
>
> I tried |*ST_BuildArea*(|geometry A|)|;  and 
> |*ST_BdMPolyFromText*(|text WKT, integer srid|)|;
>
> but the output is empty. I think it's becouse this functions may need 
> the MULTILINESTRING to be closed and it's not.
>
> Any suggestion?
>
> 2011/3/25 Javier Perez <javi.peisaco at gmail.com 
> <mailto:javi.peisaco at gmail.com>>
>
>     Hi Marc-Andre!
>
>     I think this usefull.
>
>     Thanks a lot!
>
>     Regards
>
>     2011/3/25 Morin, Marc-André <Marc-Andre.Morin at dfo-mpo.gc.ca
>     <mailto:Marc-Andre.Morin at dfo-mpo.gc.ca>>
>
>         *Hi,*
>         **
>         *This is the recipe I found in the past to get it done:*
>         **
>         http://postgis.refractions.net/pipermail/postgis-users/2008-May/019901.html
>         It worked well for me.
>         Regards,
>         Marc-André
>         ------------------------------------------------------------------------
>         *De :* postgis-users-bounces at postgis.refractions.net
>         <mailto:postgis-users-bounces at postgis.refractions.net>
>         [mailto:postgis-users-bounces at postgis.refractions.net
>         <mailto:postgis-users-bounces at postgis.refractions.net>] *De la
>         part de* Javier Perez
>         *Envoyé :* March 25, 2011 7:35 AM
>         *À :* postgis-users at postgis.refractions.net
>         <mailto:postgis-users at postgis.refractions.net>
>         *Objet :* [postgis-users] MULTILINESTRING to MULTIPOLYGON
>
>         Hi!,
>
>         In my app I get a MULTILINESTRING and want to insert it as
>         MULTIPOLYGON. I think there's an easy way but I did't found,
>         can anyone bring some light?
>
>
>         Thanks in advance
>
>
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