| Re: Array indexing problem: Appreciated [message #37857] |
Thu, 29 January 2004 05:42 |
Ken Knapp
Messages: 14
Registered: April 2003
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Junior Member |
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My 2 cents-
I won't say I "enormously appreciate" it, but here is how I have found
it useful. Consider needing to calculate a spatial standard deviation
for an image. Rather than loop over the dimensions of the image, I loop
over the size of the standard deviation window. I use this array
notation so I don't have to worry about the calculations at the edges.
here's my code. If there is a simpler way to do this without the
"enormously appreciated" "feature" then let me know ;-)
-Ken
function spatstdev,input,n
s=size(input)
nx = s(1)
ny = s(2)
var = fltarr(nx+2*n,ny+2*n)
mask= intarr(nx+2*n,ny+2*n)
var(n:n+nx-1,n:n+ny-1) = input
mask(n:n+nx-1,n:n+ny-1) = 1
ii = lindgen(nx,ny)
i = (ii mod nx) + n
j = floor(ii / nx) + n
x2 = fltarr(nx+2*n,ny+2*n)
x = fltarr(nx+2*n,ny+2*n)
nn = fltarr(nx+2*n,ny+2*n)
for ii = -n,n do begin
for jj = -n,n do begin
x2 = x2 + var[i+ii,j+jj]^2
x = x + var[i+ii,j+jj]
nn = nn + mask[i+ii,j+jj]
endfor
endfor
std = sqrt((x2 - ((x^2)/nn)) / (nn-1))
return,std
end
--
***** to reply remove the _REMOVE_ *****
Ken Knapp Ken.Knapp@_REMOVE_noaa.gov
Remote Sensing and Applications Division
National Climatic Data Center
151 Patton Ave
Asheville, NC 28806
828-271-4339 (voice) 828-271-4328 (fax)
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