[R-sig-Geo] calculate "regional" slope

[Dominik Schneider]

Thanks for the suggestion Chris.  I'm familiar with gdaldem, which
raster::terrain is based on, to compute slope from a dem. I now realize
that my example isnt a good one because neighbors=8 would achieve what I
described. However I actually want some flexibility such that I can
specifiy neighbors=16 so that it uses the next "ring" of cells.

I played around with focal() with weight argument =
matrix(rep(c(1,0,0,0,1),5),byrow=T) but couldn't figure out how to solve
for a directional slope.

On Fri, Feb 19, 2016 at 4:09 AM, chris english <
englishchristophera at gmail.com> wrote:

> Dominik,
>
> r <- raster(nrows=22, ncols=20, xmn=-58, xmx=-48, ymn=-33, ymx=-22)
>  vals <- sample.int(1e3,440)
> r[ ] <- vals
> #raster::terrain
> terr_r <- terrain(r, opt='slope', unit='degrees', neighbors=8)
> Ah, but it appears you want up sampling to 1.5 degrees rather than 0.5 deg.
> so maybe spatial.tools::projectRaster_rigorous then raster:terrain.
>
> I'm inclined to end that last so maybe with a question mark. Sorry for an
> essentially inconclusive response but I was happy to find terrain in any
> case.
> Chris
>
> On Fri, Feb 19, 2016 at 2:59 AM, Dominik Schneider <
> Dominik.Schneider at colorado.edu> wrote:
>
>> I need to calculate slope at different scales. In the case below, r is a
>> 0.5deg resolution raster and I want the slope for 1.5 deg centered on each
>> of those 0.5 deg pixels. I'm trying to estimate which side of mountain
>> range each pixel is on. So the resulting raster would have the same number
>> of pixels as r. The edges can be NA.
>> any suggestions would be appreciated. Thanks
>>
>>
>> r <- raster(nrows=22, ncols=20, xmn=-58, xmx=-48, ymn=-33, ymx=-22)
>> setValues(r,rnorm(440))
>>
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