[R-sig-Geo] help me find a buffer around a polygon

[Robert J. Hijmans]

Roman, Have you tried combinations of the functions 'edge', and
'distance' (and perhaps adjacency, if the 'amount' is expressed in
cells rather than distance). Robert

On Thu, Nov 18, 2010 at 5:58 AM, Roman Luštrik <roman.lustrik at gmail.com> wrote:
> Dear list,
>
> I've been searching around and I continue to do so, but in the mean time I'm
> seeking your advice on how to improve my approach.
>
> I'm using raster package and I'm trying to find cells around (let's call it
> a buffer) and inside a polygon. These subsetted cells are used for
> calculations later on. I'm basically trying to "grow" a polygon by a certain
> specified amount.
>
> I have created a raster with values derived as 1:ncell(my.object), where
> each value actually represents cell number and in a sense, position. This is
> the playground for my polygon.
>
> So far, I've approached this by:
> - find cell values inside the polygon (former raster::polygonValues)
> - find cell values within the buffer of SpatialLines object (made from the
> above polygon) (former raster::lineValues)
> - find unique cell values from the above results
>
> The problem is that finding buffers around each cell on a line (second step)
> is pretty RAM greedy. Would there be a more efficient way of "growing" a
> polygon, preferably without using external software?
>
>
> Cheers,
> Roman
>
>
>
> --
> In God we trust, all others bring data.
>
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