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Re: checking for connectedness of a given set of pixels [message #73514 is a reply to message #73430]

Sun, 14 November 2010 13:56

guillermo.castilla.ca is currently offline

guillermo.castilla.ca
Messages: 27
Registered: September 2008

Junior Member

On Nov 8, 3:22 pm, James <donje...@gmail.com> wrote:

> One problem is that LABEL_REGION runs over a whole array even if it is
> mostly empty (sparse). This is why LABEL_REGION might be slow for
> your task - it could be doing a lot of unnecessary extra work.

Thanks a lot James, very insightful comments, and very nice piece of
code :). After giving it some more thought, I found out that there is
an IDL function called REGI0N_GROW that may be faster than
LABEL_REGION for this purpose when the minimum bounding box for the
input set of pixels is large. I have modified your function to include
the former as an alternative method (below). I'll do some tests and
report back (hopefully within this year :).

function ISCONNECTED, points, method=method, _extra=ex
mins = min(points, max=maxs, dimension=2)-1
dims=maxs-mins+3
npts= n_elements(points)/2
indices= points - mins # replicate(1, npts)
indices= indices[0,*] + dims[0]*indices[1,*]
arr = bytarr(dims)
arr[indices] = 1B
if ~keyword_set(method) then $
return, max(label_region(arr, _extra=ex)) le 1 $
else return, n_elements(region_grow( $
arr, indices[0], thresh=[1B,1B], _extra=ex)) eq npts
end

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[Message index]

		Re: checking for connectedness of a given set of pixels By: David Fanning on Wed, 03 November 2010 06:35
		Re: checking for connectedness of a given set of pixels By: guillermo.castilla.ca on Wed, 03 November 2010 06:32
		Re: checking for connectedness of a given set of pixels By: David Fanning on Tue, 02 November 2010 15:14
		Re: checking for connectedness of a given set of pixels By: guillermo.castilla.ca on Tue, 02 November 2010 15:06
		Re: checking for connectedness of a given set of pixels By: David Fanning on Tue, 02 November 2010 13:37
		Re: checking for connectedness of a given set of pixels By: James[2] on Mon, 08 November 2010 11:22
		Re: checking for connectedness of a given set of pixels By: guillermo.castilla.ca on Sun, 14 November 2010 13:56
		Re: checking for connectedness of a given set of pixels By: guillermo.castilla.ca on Mon, 03 January 2011 13:50

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