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Re: Incremental variable names? [message #37872]

Wed, 04 February 2004 01:34

Chris Lee
Messages: 101
Registered: August 2003

Senior Member

In article <BC4475B7.18FD5%greenberg@ucdavis.edu>, "Jonathan Greenberg"
<greenberg@ucdavis.edu> wrote:

> I'm trying to optimize this algorithm for use with large images.
> ENVI/IDL work well if you extract a single line of an image at a time
> (line = y axis, by the way). For a circular mask, however, I'd need to
> extract at least as many lines as the maximum circular diameter (e.g. If
> my circle is 3 pixels in radius, I need to pull out 7 lines of data to
> figure out the values along the ring).
> It occurred to me (and tell me if I'm wrong), that while I CAN extract
> the line I'm working on +/- 3 lines from the image each time, this seems
> like an awful waste of I/O, when in reality the next line will use all
> but one of the previous extracted rows (e.g. I just need to read the
> next line in, and delete the current top line to free up memory).
> Creating arrays of the lines would require rewriting the arrays each
> time (e.g. Arraynew = (arrayold(2:7),newline) -- I know this isn't idl
> code, but you get the idea) which seems slower than just having 7 named
> variables (line1,line2,...line7), doing my calculation, then deleting
> line1, and adding line8 and repeating.
> No? Is there a better way of "preserving" the data I've already read
> from the HD than using incremental variable names? --j
> On 2/2/04 1:45 PM, in article

If I understand your method correctly.....Create a 2D array with the
dimension of (radius, line length). Each time you read in a new line..

array=fltarr(radius, line_length)
input=fltarr(line_length)
openr, file, "filename", /get_lun
counter=0L
cmax=2*radius+1
while(not eof(file)) do begin
readu,file, input
array[counter mod cmax,0]=input
array=shift(array, 1,0) ;;;;This could be wrong, try -1,0...
result=do_stuff(array)
counter=counter+1
endwhile

free_lun, file

; I think that would work..

Of course, if I understand this whole ring thing, your doing this with
every point on your image? If you are, the function DO_STUFF above (your
semi-variance code) had better be vectorised along the line_length.

Chris.

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[Message index]

		Re: Incremental variable names? By: Chris Lee on Wed, 04 February 2004 01:34
		Re: Incremental variable names? By: Jonathan Greenberg on Mon, 02 February 2004 21:46
		Re: Incremental variable names? By: condor on Mon, 02 February 2004 13:45
		Re: Incremental variable names? By: MKatz843 on Mon, 02 February 2004 08:52
		Re: Incremental variable names? By: btt on Mon, 02 February 2004 05:57
		Re: Incremental variable names? By: David Fanning on Sun, 01 February 2004 20:57
		Re: Incremental variable names? By: David Fanning on Sun, 01 February 2004 20:55
		Re: Incremental variable names? By: mmeron on Sun, 01 February 2004 20:51

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