[R-sig-Geo] knearneigh() computing efficiency on large datasets

[Robert J. Hijmans]

You can try one of the 'focal' functions of the raster package on
R-Forge. Not particularly fast either, but probably much faster that
what you have now. Robert

On Thu, Jan 28, 2010 at 11:16 PM, Pierre Roudier
<pierre.roudier at gmail.com> wrote:
> Dear list,
>
> I am processing gridded data like DEMs, imported in R from geotiff
> files. Of course, such data is regularly gridded, but very often with
> NA values. In the framwork of some tests, I have to generate a
> neighbourhood of the DEM, so that to extract local extrema of the
> layer. For this task, I wrote a function based on  the knearneig()
> function from the spdep package, with k=4 or k=8, to generate and
> analyse the neighbourhood of each point.
>
> Unfortunately, I often have to process big datasets (let's say grids
> with between  50,000 and 350,000 points), and that's working but
> knearneigh() takes *hours* to process.
>
> Does anybody would have any suggestion to improve the efficiency of this step ?
>
> Thanks,
>
> Pierre
>
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