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Re: Rapid "moving windows" access in IDL? [message #37842 is a reply to message #37824]

Fri, 30 January 2004 06:09

Chris Lee
Messages: 101
Registered: August 2003

Senior Member

In article <BC3F7CE8.18DCE%greenberg@ucdavis.edu>, "Jonathan Greenberg"
<greenberg@ucdavis.edu> wrote:

> Ok, now to make this a bit more confusing -- in practice, what I will
> actually be doing is selecting all pixels at about a given distance from
> the center point, creating a ring of pixels that will be used for the
> semivariogram. Getting back to an earlier question, is the array
> subscripting an inherently slow process, and are there "better" and
> "worse" ways of accessing array elements given an x,y coordinates? More
> thoughts?
> --j

Why not make a ring of 1s and 0s..e.g.

nx=100
ny=100

dist=shift(dist(nx,ny),nx/2, ny/2)
mask=fltarr(nx,ny)
mask[*]=0.0
outer=25
inner=23

mask[where(dist lt outer)]=1.0
mask[where(dist lt inner)]=0.0

;mask contains a ring of 1s

ring = mask * data .
OR
ring = data[where(mask eq 1)]

Chris.

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[Message index]

		Re: Rapid "moving windows" access in IDL? By: Craig Markwardt on Fri, 30 January 2004 14:55
		Re: Rapid "moving windows" access in IDL? By: Chris Lee on Fri, 30 January 2004 06:09
		Re: Rapid "moving windows" access in IDL? By: Jonathan Greenberg on Fri, 30 January 2004 03:15
		Re: Rapid "moving windows" access in IDL? By: Craig Markwardt on Thu, 29 January 2004 22:01
		Re: Rapid "moving windows" access in IDL? By: mchinand on Thu, 29 January 2004 20:33
		Re: Rapid "moving windows" access in IDL? By: Jaco van Gorkom on Sun, 01 February 2004 14:20

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