wow, thanks a lot!
indeed, much much nicer!
thanks again,
Denis
On 21. 11. 13 15:47, Nicolas Ribot wrote:
Thanks for the explanation.
You could correct the multipolygons in one step, by using the
st_buildArea function, that "merges" a linework of linestrings,
preserving holes.
To extract polygons boundaries as linestring, st_boundary() is very handy:
The "bad_multipg" table contains invalid multipolygons with adjacent
parts (http://imgur.com/MP6Cy4f)
select gid, st_buildArea(st_boundary(geom))
from bad_multipg
group by gid;
Gives: http://imgur.com/RqlowFI
Nicolas
On 21 November 2013 13:50, Denis Rouzaud <[email protected]> wrote:
Hi Nicolas,
I edit my multi polygons in QGIS, and you're right the geometry becomes
invalid if some parts have adjacent segments.
In a simple case, I would have a multi polygons with 3 parts with 2 parts
adjacent.
http://imgur.com/zvxPFeR
Although the geometry is invalid, my intention is to make it valid, and
therefore merge the two parts, which is impossible in QGIS - AFAIK.
So my intention was to save the geometry as this, and make it valid by a
command.
I could achieve this with a function:
CREATE OR REPLACE FUNCTION distribution.simplemultipoly(geom geometry)
RETURNS geometry AS
$BODY$
DECLARE
num_geom integer;
BEGIN
SELECT ST_NumGeometries(geom) into num_geom;
SELECT
ST_Multi(ST_CollectionHomogenize(ST_Union(ST_GeometryN(geom,n))))
FROM generate_series(1,num_geom) n
INTO geom;
RETURN geom;
END;
$BODY$
LANGUAGE plpgsql;
But I wondered if there was a more direct way.
Cheers,
Denis
On 21. 11. 13 12:42, Nicolas Ribot wrote:
Hi Denis,
In your example, I don't understand how the parts of your
multipolygons can be adjacent. Are they valid ?
Do you have a visual example ?
Thank you
Nicolas
On 21 November 2013 07:32, Denis Rouzaud <[email protected]> wrote:
Hello Rémi,
I was hoping a simplest request without enabling topology but thanks anyway!
Cheers,
Denis
On 20. 11. 13 18:26, Rémi Cura wrote:
From what I understand of your needs, Postigs topology was designed for
this.
Cheers,
Rémi-C
2013/11/20 Denis Rouzaud <[email protected]>
Hi all,
I am drawing some multipolygons in QGIS and sometimes, I have parts of
them which are adjacent and I'd like to homogenize them to have less parts
and no adjacent parts.
I could do this with a quite complex method:
1. get the number of parts Z:
SELECT ST_NumGeometries(geometry) FROMmytable WHERE id=123;
2. do the simplification using ST_CollectionHomogenize:
SELECT
ST_Multi(ST_CollectionHomogenize(ST_Union(ST_GeometryN(geometry,n)))) FROM
mytable CROSS JOIN generate_series(1,Z) n WHERE id = 123;
3. update manually the result in the table (copy paste).
Does someone has something more straightforward???
Thanks a lot!
Best regards,
Denis
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