On Wed, 4 Nov 2015, Roger Bivand wrote:
On Wed, 4 Nov 2015, Eduardo Diez wrote:
Is there any way of doing this or should i forget it and go on using GRASS
through rgrass7?
I suggest working with Emmanuel Blondel (cleangeo maintainer) to extend
cleangeo (also suggested in an earlier thread today, with apologies to
Emmanuel for picking on him!). That package already uses rgeos, and is a
logical place to put GRASS v.clean-like functionality (maybe even
encapsulating using GRASs via rgrass7 and a throwaway location).
At the moment it is messy, though some rgeos internals do do something like
this, but it isn't exposed to users.
A possibility is to use:
set_RGEOS_polyThreshold(1e-2) # for example
set_RGEOS_warnSlivers(TRUE)
shows the remaining slivers, and:
set_RGEOS_dropSlivers(TRUE)
drops them when using for example:
t1 <- gBuffer(<your_object>, byid=TRUE, width=0)
A buffer of zero width should not have side-effects, but your mileage may
vary. It will only remove slivers, not dangles. I haven't tried it when it
also finds a Polygons object under the threshold, which was your initial
problem.
Roger
Roger
Thanks
2015-10-19 15:03 GMT-03:00 Eduardo Diez <eduardod...@gmx.com>:
> Ok. So here's a link to a zip file that contains two shapefiles:
> - pol_to_be_cleaned: the layer from which i'd like to remove small
> polygons
> - pol_cleaned: the layer cleaned with the function v.clean rmarea
>
> http://1drv.ms/1GmRWS7
>
> The threshold i used for cleaning was 3000 (meaning 3000 squared
> meters).
>
> Although i do project it before sending it to GRASS, according to the
> official help page it should be able to handle it:
> "Threshold must always be in square meters, also for latitude-longitude
> locations or locations with units other than meters"
>
> Thanks
>
> 2015-10-19 8:28 GMT-03:00 Roger Bivand <roger.biv...@nhh.no>:
>
> > On Fri, 16 Oct 2015, Eduardo Diez wrote:
> >
> > Dear list,
> > > I'm willing to know if any knows a way of performing tha same thing
> > > i'm
> > > doing through rgrass7 with GRASS when I execute the function v.clean
> > > with
> > > "rmarea" as the tool argument. That is:
> > >
> > > "The rmarea tool removes all areas <= thresh. The longest boundary
> > > with
> > > an
> > > adjacent area is removed or all boundaries if there is no adjacent
> > > area.
> > > Area categories are not combined when a small area is merged with a
> > > larger
> > > area."
> > >
> > > Basically i have raster of zones within a field. I convert it to
> > > SpatialPolygonsDataFrame and in order to leave only the more
> > > important/meaningful ones i remove the small/sliver with this tool.
> > > In
> > > general it works fine but having to call an external software with a
> > > specific version makes the script less portable and you have to be
> > > careful
> > > with updates and such. Also you have to write rasters and shapefiles
> > > back
> > > and forth as GRASS can't work with in-memory objects.
> > >
> >
> > Could you please provide an example of a built-in or contributed data
> > set
> > (URL, not attachment) with the slivers you mention, so that we know
> > that we
> > are addressing your problem? I don't think that:
> >
> > https://cran.r-project.org/web/packages/cleangeo/index.html
> >
> > does this, as it seems to try to repair broken geometries.
> >
> > Also note that you need to specify that the area threshold is in a
> > square
> > planar metric - dropping slivers in unprojected geometries may be more
> > complicated.
> >
> > Roger
> >
> >
> > > Does someone know a way of doing this in plain R?
> > >
> > > Thanks
> > >
> > > [[alternative HTML version deleted]]
> > >
> > > _______________________________________________
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> > > R-sig-Geo@r-project.org
> > > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> > >
> > >
> > --
> > Roger Bivand
> > Department of Economics, Norwegian School of Economics,
> > Helleveien 30, N-5045 Bergen, Norway.
> > voice: +47 55 95 93 55; fax +47 55 95 91 00
> > e-mail: roger.biv...@nhh.no
> >
> >
>
--
Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; fax +47 55 95 91 00
e-mail: roger.biv...@nhh.no
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