[postgis-users] Topology: cannot delete slivers (or gaps)

[Rémi Cura]

Note you could have directly exported into postgis topology, which is slow
but very convenient (stil faster than postgis topology conversion).
I'm not a grass user,
from what I understood you have to use the "-l" switch in the command "
*v.out.postgis*"

Glad it helped =)
Cheers,
Rémi-C

2014-11-10 13:56 GMT+01:00 Humberto Cereser Ibanez <
humberto at pastoraldacrianca.org.br>:

> I was with the same problem, getting gaps in some adjacent polygons
> while trying to simplify polygons with Postgis.
> Thank Guillaume / Rémi / Sandro by the contributions.
> Illuminated by this thread, I created a script in which I avoided gaps
> from the bad polygons. Really the most appropriate tool, GRASS, became
> this work easier.
>
> On Fri, 2014-11-07 at 13:14 -0800, Guillaume Drolet wrote:
> > I finally finished cleaning my topology, using a mix of SQL commands,
> > functions, and also using Sandro's QGIS topology editor plugin.
> >
> > In parallel, I also tried going the GRASS route, importing my original
> > shapefile in GRASS and applying the cleaning function (v.clean ...) as
> > suggested by Remi. I injected the result into PostGIS and created a
> > topology. Most of the 23 slivers were there in the topology so one of two
> > things: 1) GRASS didn't fix them (maybe I didn't choose an appropriate
> > tolerance) or 2) they were created by PostGIS when building the topology.
> Simplifying polygons with QGIS and GRASS
>    Note: SRID = 4326
> 1) Open shapefile in QGIS
> 2) Create New Mapset
>     Import Extent from opened Shapefile
> 3) Check the smaller area of the polygons involved
>     select ST_Area (geo_polygon) from table order by
> ST_Area(geo_polygon);
>     Smaller area = 0.005471
> 4) Import shapefile into GRASS
>     v.in.ogr dsn = /home/humberto/shapefiles/pr/41MUE250GC_SIR.shp
> output = prGrass snap = 0.0001 min_area = 0.004 -o
>     Settings of parameters: Snapping threshold for boundaries = 0.0001
> and Minimum size of area to be imported (squere units) = 0.004
>     Note: The 0.004 value was chosen to allow importing of the smaller
> area = 0.005 and all areas greater than it, avoiding any small ring that
> would be arising from this importing.
> 5) Simplify the Shapefile polygon imported
>     v.generalize input=prGrass at elimSlivers type=area layer=1 -c
> type=boundary method=douglas threshold=0.001 look_ahead=7 reduction=50
> slide=0.5 angle_thresh=3 degree_thresh=0 closeness_thresh=0
> betweeness_thresh=0 alpha=1.0 beta=1.0 iterations=1
> output=prGrassGeneralized
>     Settings of parameters: threshold = 0.001
>     Note: the threshold value 0.001 was chosen by trial
> 6) Export the simplified polygon to Postgis
>    v.out.ogr.pg.py input=prGrassGeneralized at elimSlivers type=area
> layer=1 olayer=prgeneralized database=simp22 host=127.0.0.1 port=5432
> user=name password=nonono
>
> >
> > Anyway, I got what I finally got what I need, thanks a lot to all of you
> who
> > helped me.
> >
> > I'm gonna ask you one last thing if I may: I want to replace the original
> > geom column (i.e. that used to build the topogeom) with a topologically
> > correct one, and keep all the associated ecological attributes. Is this
> the
> > right way to do it:
> >
> > UPDATE syshiera.de_20k SET geom = topogeom::geometry; ?
> >
> > Thanks.
> >
> >
> >
> > --
> > View this message in context:
> http://postgis.17.x6.nabble.com/Topology-cannot-delete-slivers-or-gaps-tp5007250p5007286.html
> > Sent from the PostGIS - User mailing list archive at Nabble.com.
> > _______________________________________________
> > postgis-users mailing list
> > postgis-users at lists.osgeo.org
> > http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
>
> Thanks,
>
> Humberto
>
> _______________________________________________
> postgis-users mailing list
> postgis-users at lists.osgeo.org
> http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/postgis-users/attachments/20141112/1389ff27/attachment.html>