[postgis-users] Help with a multipolygon filtering function

[Nicklas Avén]

I should ignori it, but I had to correct a typo, the last query I think
should be:

Select st_collectionextract(st_collect(whole_table.the_geom), 3)
from 
(Select (st_dump(the_geom)).geom as the_geom,(st_dump(the_geom)).path as
the_path, id from myTable) as whole_table
 left join
(SELECT a.the_path, a.id FROM 
(SELECT (st_dump(the_geom)).geom as the_geom ,(st_dump(the_geom)).path
as the_path, id from myTable) as a
left join 
(SELECT (st_dump(the_geom)).geom as the_geom, id from myTable) as b
on st_dwithin(a.the_geom, b.the_geom, theDistance)
where b.id is null) too_far_away 
on whole_table.id=too_far_away.id and
whole_table.the_path=too_far_away.path
where too_far_away.path is null
group by whole_table.id;


/Nicklas



> I want to clean up some multipolygons and remove any polygons over a
> certain
> distance by using a postgis function.
> 
> This is the closest I've come:
> 
>     CREATE OR REPLACE FUNCTION filter_polygons_within(geometry, double
> precision)
>       RETURNS geometry AS
>     $BODY$
>     SELECT ST_Multi(ST_Collect(final_geom.poly)) AS filtered_geom
>     FROM (
>         SELECT DISTINCT a.poly
>         FROM (
>             SELECT ST_GeometryN(ST_Multi($1), generate_series(1,
> ST_NumGeometries(ST_Multi($1)))) AS poly,
>             (SELECT ST_GeometryN(ST_Multi($1), generate_series(1,
> ST_NumGeometries(ST_Multi($1))))) as poly_b
>         ) AS a
>         WHERE a.poly != a.poly_b
>         AND ST_DWithin(a.poly, a.poly_b, $1)
>     ) as final_geom
>     $BODY$
>     LANGUAGE 'sql' IMMUTABLE;
> 
> However, the where clause isn't working for me - any ideas on how to
> achieve
> this?  I'm not sure on how to compare all polygons with each other, I
> know
> how to get a list of polygons;
> 
>     ST_GeometryN(ST_Multi($1), generate_series(1,
> ST_NumGeometries(ST_Multi($1))))
> 
> I'm just not sure how to compare each one with another and return the
> distinct polygon results.
> 
> Thanks in advance,
> 
> Ross 
> 
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