Yeah, it's a relatively newly discovered syntax that works very well.
http://postgis.refractions.net/documentation/manual-svn/ST_Dump.html
Cheers,
Kevin
Frank Durstewitz, Emporis GmbH wrote:
Hi Kevin,
yes, that looks good. I was on that way, but could not figure out, how
to get the geometry out of the dump rows.
Very nice this one, i have never seen this ".geom" (and still could not
find it somewhere in the docs?).
Many thanks!
Kindly regards, Frank
Kevin Neufeld am 24.10.2008 20:44:
What about something like this:
SELECT ST_Collect(geom)
FROM (
SELECT (ST_Dump(geom)).geom
FROM my_multi_polygon_table) AS foo
WHERE ST_Y(ST_Centroid(geom)) <= 0;
Explode the multipolygon into individual polygons using ST_Dump, and
ST_Collect the ones back up again where the centroid falls within some
specification.
-- Kevin
Frank Durstewitz wrote:
Hello list,
i must remove from multipolygon some polygons, for example remove all
polygons from "russia", where latitude of centroid of polygon is <= 0
(in this case the part of russia which is near alaska).
I think this should be possible (ST_Dump...), but i cannot find any
way to do so.
Deleting the vertices by hand via a desktop gis is painfull slow and
will take ages - i tried this and need ~ 5 minutes for a very small
island of ~ 20 points... (i found no desktop gis where i can select
multiple vertices by a bounding box and delete them at once).
Thanks,
Frank
ST_Summarize gives
MultiPolygon[BS] with 1393 elements
Polygon[] with 1 rings
ring 0 has 15 points
...
Polygon[] with 1 rings
ring 0 has 25 points
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