[postgis-users] Can you rebuild a multipolygon from rings?

[Ben Madin]

Thanks strk,

but I'm still confused. If I don't select the .geom component, I can't dumprings... when I do, I end up with 90 rows in a table of geometry dumps.

# select id, (the_geom).path, st_astext((the_geom).geom) from phl2 where id = 58;
 id | path |                                                  st_astext                                                   
----+------+--------------------------------------------------------------------------------------------------------------
 58 | {57} | POLYGON((126.023966 8.568675,126.023895 8.56901,126.013809 8.570289,126.023912 8.56893,126.023966 8.568675))
(1 row)

# select id, ((the_geom).path), st_isvalidreason((the_geom).geom) from phl2 where st_isvalid((the_geom).geom) is false;
NOTICE:  Self-intersection at or near point 126.024 8.56893
 id | path |                  st_isvalidreason                   
----+------+-----------------------------------------------------
 58 | {57} | Self-intersection[126.02391195391 8.56893000619979]


which is the polygon ring I want to delete

I can delete it, but I now want to insert this polygon (the remaining 89 rows) back into my table of polgons (the dump from the first step), and then turn them back into a multipolygon. In fact, I can do the last step. But I can't get the geometry dump back into the polygons table in geometry dump format. 

Maybe I'm trying to do this wrong, but there must be a function I haven't found?

cheers

Ben



On 21/10/2011, at 3:17 PM, Sandro Santilli wrote:

> On Fri, Oct 21, 2011 at 01:33:43PM +0800, Ben Madin wrote:
> 
>> But rebuilding the multipolygons is not so simple (for me) - I need to re-aggregate the remaining rings into a geometry dump to reinsert into the other dumped polygons to rebuild the multipolygon.
> 
> ...
> 
>> insert into phl (the_geom) select ((st_dump(the_geom))) from summ.ctybnda where year=2005 and ccode like 'PHL';
> 
> ...
> 
>> insert into phl2 (the_geom) select st_dumprings(((the_geom).geom)) from phl where id = 2601;
> 
> 
> You're stripping out the "path" component of output from st_dump
> and st_dumprings. Those are the keys to your later rebuilding.
> 
> --strk; 
> 
>  ()   Free GIS & Flash consultant/developer
>  /\   http://strk.keybit.net/services.html
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