Hi,
Alternatively you could have a look at the function "terrain" in the
raster package, it can calculate the slope for you using different
algorithms, not sure if the one below is included though.
For typical spatial requests like this, you could also use the
mailing-list r-sig-geo.
Cheers,
Jon
On 01-Dec-11 14:27, Jean V Adams wrote:
jjcabrera20 wrote on 12/01/2011 04:02:47 AM:
Hello everyone in the forum
For introducing myself I would say I have a basic knowledge of R.
Now I am intended to implement a flood algorithm using R. I have some
MatLab
experience doing these, and as an example to explain more or less what I
want, I have a m code to calculate the slope from a Digital elevation
model:
slope=zeros(row,col);
for i=2:row-1
for j=2:col-1
dzdx=(raster(i,j+1)-raster(i,j-1))/(2*res);
dzdy=(raster(i+1,j)-raster(i-1,j))/(2*res);
slope(i,j)=sqrt(dzdx^2+dzdy^2);
end
end;
The question is to know how to do the similar procedure on R. All
suggestions are welcome
Thanks
All best,
Jorge
PD:I am using R on windows system 64 bits
If I am interpreting your code correctly (I don't use MatLab myself),
something like this should give you the same result in R:
# example matrix of heights
raster<- matrix(runif(20, 10, 30), nrow=4, ncol=5)
# example resolution
res<- 8.5
# dimensions of matrix
drast<- dim(raster)
# for every non-boundary point in the matrix,
# calculate the distances between its adjacent columns (dzdx) and rows
(dzdy)
dzdx<- raster[2:(drast[1]-1), 3:drast[2]] - raster[2:(drast[1]-1),
1:(drast[2]-2)]
dzdy<- raster[3:drast[1], 2:(drast[2]-1)] - raster[1:(drast[1]-2),
2:(drast[2]-1)]
# calculate the slope from these distances and the resolution
slope<- sqrt(dzdx^2 + dzdy^2) / (2*res)
Jean
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