[postgis-users] Making one out of several connected polygons?

[Simon Schneider]

Great seems to do exactly what I need. But when I tried to test it with 
some simple samples:

create table objects
(
   name varchar(15) not null primary key,
   parent varchar(15),
   type varchar(15) not null
);
select addgeometrycolumn('objects','geom3d',-1,'POLYGON',3);

insert into objects(name, type, geom3d) values('Room01', 'room', 
(GeomFromEWKT('POLYGON((0 0 0, 10 0 0, 10 10 0, 0 10 0, 0 0 0))')));
insert into objects(name, type, geom3d) values('Room02', 'room', 
(GeomFromEWKT('POLYGON((10 0 0, 20 0 0, 20 10 0, 10 10 0, 10 0 0))')));

select astext(geom3d) from (select geomunion(objects.geom3d)::geometry 
from objects) as foo;

it says: ERROR: column "geom3d" does not exist


Did I miss something or what's going wrong?


Nicolas Ribot schrieb:
> Try to  geomunion() your polygons.
> It will create a multipolygon where touching polygons will be unioned.
> then, use dump()  on the geomunion to extract each polygon.
> 
> Example:
> the polygon table contains:
> 
> test=# select id, astext(geometry) from tpoly2;
>  id |                               astext
> ----+--------------------------------------------------------------------
>   1 | POLYGON((166 272,107 210,145 142,218 158,209 215,182 240,166 272))
>   2 | POLYGON((242 118,218 158,145 142,167 104,242 118))
>   3 | POLYGON((76 161,145 142,167 104,112 78,76 161))
>     | POLYGON((284 174,283 112,320 124,295 129,302 156,284 174))
> (4 rows)
> 
> The query to extract unioned polygon based on a common edge:
> 
> select astext(geom(dump(geom))), path(dump(geom))
> from (select geomunion(t1.geometry)::geometry as geom
>         from tpoly2 t1
>         ) as foo;
> 
> Leads to this result:
>                                             astext
>                          | path
> -------------------------------------------------------------------------------------------------+------
>  POLYGON((284 174,302 156,295 129,320 124,283 112,284 174))
>                           | {1}
>  POLYGON((76 161,145 142,107 210,166 272,182 240,209 215,218 158,242
> 118,167 104,112 78,76 161)) | {2}
> (2 rows)
> 
> (see polygon.png and result.png images done with openjump)
> 
> HTH
> 
> Nicolas
> On 01/02/2008, Simon Schneider <Kallas at gmx.de> wrote:
>> Hi,
>>
>> I've several polygons wich are all connected by at least one line and
>> I'm looking for a way to make one big polygon which contains all the
>> others. In other words the shape of the polygoncluster.
>>
>> I've been locking around for quite a while but I found no way to solve
>> this within postgis.
>>
>>
>> Cheers,
>> Simon
>> _______________________________________________
>> postgis-users mailing list
>> postgis-users at postgis.refractions.net
>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>>
>>
>> ------------------------------------------------------------------------
>>
>>
>> ------------------------------------------------------------------------
>>
>>
>> ------------------------------------------------------------------------
>>
>> _______________________________________________
>> postgis-users mailing list
>> postgis-users at postgis.refractions.net
>> http://postgis.refractions.net/mailman/listinfo/postgis-users