#2368: Python version of r.grow does not support shrinking
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Reporter: wenzeslaus | Owner: grass-dev@…
Type: | Status: new
enhancement |
Priority: minor | Milestone: 7.2.0
Component: Raster | Version: svn-trunk
Resolution: | Keywords: r.grow, r.grow.distance, r.buffer,
CPU: | r.buffer.lowmem
Unspecified | Platform: Unspecified
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Comment (by mmetz):
Replying to [comment:12 mmetz]:
> Replying to [comment:9 neteler]:
> > Replying to [comment:7 neteler]:
> > > Replying to [comment:6 mmetz]:
> > > > Replying to [comment:3 glynn]:
> > > > > The easiest change would be to have an "invert" flag which
caused the distance= map to contain the distance from the nearest null
cell (currently, it's the distance from the nearest non-null cell, so the
non-null cells themselves have a distance of 0).
> > > >
> > > > Attached is a minimally invasive patch to add a new flag to
r.grow.distance, calculating the distance to the nearest null cell.
> > >
> > > Patch applied to trunk in r67620.
> >
> > Can I backport this to 7.2.0? Again I need a negative buffer...
>
> This is a new feature and as such does not qualify for backport.
>
> If you want to shrink you can use
>
> {{{
> r.mapcalc "input_inv = if(isnull(input), 1, null())"
> r.grow input=input_inv
> }}}
I meant r.grow.distance, not r.grow.
>
> Replying to [comment:10 neteler]:
> > Just tested r.grow with a negative radius and the following error
occurs:
> > {{{
> > # NC sample dataset
> > v.in.region box
> > v.to.rast input=box output=box use=val val=1
> >
> > r.grow input=box output=box_shrink radius=-20.01
> > }}}
>
> The example is wrong because there are no NULL cells in the current
region for the input raster. When growing, for each NULL cell the distance
to the nearest non-NULL cell is calculated. When shrinking, for each non-
NULL cell the distance to the nearest NULL cell is calculated. That means
there must be both NULL and non-NULL cells in the input raster for the
current region, otherwise nothing can be grown or shrunk.
>
> The example can not work because r.grow does not support negative
distances.
Support for shrinking with negative radius added to r.grow in r69110.
Please try the example in the manual.
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Ticket URL: <https://trac.osgeo.org/grass/ticket/2368#comment:13>
GRASS GIS <https://grass.osgeo.org>