[R-sig-Geo] Speeding up raster calculations

[Jonathan Greenberg]

Franz:

I'm not sure what you mean that you can't use focal_hpc for your
problem -- it seems like your problem would be fine for use with that
function -- its a bit easier to use rasterEngine, by the way.  You can
use > 1 input raster into your functions if you are using
rasterEngine, and you can pass non-raster parameters to the function
as well.  If you had a simple set of data to test, perhaps I can help
you write the function.

As a heads up, focal window algorithms are slow, and get slower the
larger the window size.  rasterEngine/focal_hpc in spatial.tools will
use parallel processing to speed it up, however.

--j

--j

On Mon, Mar 3, 2014 at 4:27 PM, Franz Grassmann
<franz.grassmann at gmail.com> wrote:
> Dear list members!
>
> Maybe, someone has a good idea how to speed up my raster-calculation, or knows the right way how to deal with my "problem".
>
> For my master thesis, I use the focal-function and its focalWeight ("raster"-package) for some raster calculations. For every cell of my map, I sum up the "resources" of the surrounding cells by a certain weight that declines with distance (Its about foraging bees...). I got a map that holds the resources, and a certain focalWeight for every species of my model.
>
> The command code looks similar to this:
>
> result.raster <- focal(x = resource.map,
>                           fun = function(x) {sum(x)/sum(fW)},
>                           w = fW)
>
> It takes very long to create my raster, because the fW is quiet large for some species. I can't use the focal_hpc()-command, because it doesn't support the kind of focalWeight I use. For my analysis I also have to run this calculations for a number of species, seasons and scenarios.
>
> My questions: Did I choose the right way to solve my tasks, or is there another, faster way for my calculations? I hope I didn't choose the wrong package or program...
> I am no programmer, but I am very interested in this topic an would welcome every tip on how to solve this, or hint where to read/learn more about this.
>
> Best regards,
> Franz Grassmann
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-- 
Jonathan A. Greenberg, PhD
Assistant Professor
Global Environmental Analysis and Remote Sensing (GEARS) Laboratory
Department of Geography and Geographic Information Science
University of Illinois at Urbana-Champaign
259 Computing Applications Building, MC-150
605 East Springfield Avenue
Champaign, IL  61820-6371
Phone: 217-300-1924
http://www.geog.illinois.edu/~jgrn/
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