[postgis-users] Problem using ST_snap

[Alexandre Neto]

Hi Rémi,

I'm not sure If I understood your answer correctly. In the documentation of
ST_snap() <http://postgis.org/docs/ST_Snap.html> there are some simple
examples showing a polygon vertex snapping to a near by linestring (or it's
vertex). Shouldn't this be the same case.

The documentation says nothing about the use of geometry collections, maybe
that's the problem?

Thanks,

Alexandre Neto

On Wed, Sep 24, 2014 at 12:46 PM, Rémi Cura <remi.cura at gmail.com> wrote:

> Hey,
> snap is deceiptively named.
> As far as I know It just snaps points to points (or points in geometry to
> points in geometry).
> For exemple, if you draw 2 square side by side, one being bigger than the
> other, and separate theim with small distance, snap will do nothing.
> Cheers,
> Rémi-C
>
> 2014-09-24 13:41 GMT+02:00 Alexandre Neto <senhor.neto at gmail.com>:
>
>> Hello all,
>>
>> I have to tables in postgis. table one has a set of adjacent polygons
>> that covers all my area o interest, while table to have a few polygons
>> across the same area.
>>
>> Some boundaries of table 2 should snap to the table 1 polygons, but they
>> don't.
>>
>> I'm trying to use st_snap to correct this, but I'm not being able to do
>> it. There are vertices that "refuse" to change while other (just a few do).
>> I'm already using a very big tolerance.
>>
>>  Therefore I need your help to see if my query looks correct or not.
>>
>>
>> WITH snap_grid as
>> (
>> SELECT
>>     St_Collect(f.geom) as geom
>> FROM
>>     table_1 as f
>> )
>> SELECT
>>     r.gid, st_snap(r.geom,q.geom,10) as geom
>> FROM
>>     table2 as r,
>>     snap_grid as q
>> WHERE r.gid = 53
>>
>> I already tried dumping all point form the table 1 polygons, but the
>> result is "similar".
>>
>> Thanks in advance,
>>
>> Alexandre Neto
>>
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>
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