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Re: Cannot understand a part of the IDL routine!! pls help!! [message #71039 is a reply to message #70925]

Tue, 25 May 2010 06:23

Jeremy Bailin
Messages: 618
Registered: April 2008

Senior Member

On May 24, 1:26 pm, Brian Daniel <Daniels...@yahoo.com> wrote:
> On 24 May, 08:16, Jeremy Bailin <astroco...@gmail.com> wrote:
>
>
>
>
>
>> On May 23, 11:07 am, David Fanning <n...@dfanning.com> wrote:
>
>>> bala murugan writes:
>>>> The following is a part of the IDL routine for region grow. The
>>>> following three lines of code is used to define the pixels that is the
>>>> ROI pixels.
>>>> x = FINDGEN(16*16) MOD 16 + 276
>>>> y = LINDGEN(16*16) / 16 + 254
>>>> roiPixels = x + y * imgDims[0]
>
>>>> The question is how does it define the ROI pixels?
>>>> I dont see how it does........ Somebody please help me by giving a
>>>> simple and clear description.
>
>>> What is happening here is the IDL is turning one-dimensional
>>> image indices into two-dimensional image indices. Before
>>> the advent of the function Array_Indices, we always had
>>> to do this by hand. This code was obviously written in
>>> those long-ago dark days.
>
>>> Here is an article that explains this process in some
>>> detail:
>
>>> http://www.dfanning.com/tips/where_to_2d.html
>
>>> Cheers,
>
>>> David
>
>>> --
>>> David Fanning, Ph.D.
>>> Fanning Software Consulting, Inc.
>>> Coyote's Guide to IDL Programming:http://www.dfanning.com/
>>> Sepore ma de ni thui. ("Perhaps thou speakest truth.")
>
>> Incidentally, is there an in-built routine that I've missed that does
>> the reverse mapping (multi-D to 1D)? I know I've written my own and I
>> suspect others have too, but it seems like there ought to be a built-
>> in version.
>
>> -Jeremy.- Hide quoted text -
>
>> - Show quoted text -
>
> reform does the trick. For example:
> image = indgen(20,30,3)
> help, image
> IMAGE INT = Array[20, 30, 3]
> image_vector = reform(image,20*30*3)
> help, image_vector
> IMAGE_VECTOR INT = Array[1800]
>
> -Brian

Yes, you can of course use l/indgen to give you a multi-D array that
you can use for the mapping (I'm not sure what the point of the reform
is - I would just use image[4,3,0] to find out the 1D index of the
point (4,3,0)). But it requires generating an auxiliary array with the
required dimensions, which can be very wasteful of memory in the
applications where I tend to use it!

-Jeremy.

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[Message index]

		Cannot understand a part of the IDL routine!! pls help!! By: bala murugan on Fri, 21 May 2010 14:33
		Re: Cannot understand a part of the IDL routine!! pls help!! By: Brian Daniel on Tue, 25 May 2010 12:16
		Re: Cannot understand a part of the IDL routine!! pls help!! By: Brian Daniel on Tue, 25 May 2010 12:13
		Re: Cannot understand a part of the IDL routine!! pls help!! By: Jeremy Bailin on Wed, 26 May 2010 05:51
		Re: Cannot understand a part of the IDL routine!! pls help!! By: Jeremy Bailin on Tue, 25 May 2010 06:23
		Re: Cannot understand a part of the IDL routine!! pls help!! By: Brian Daniel on Mon, 24 May 2010 11:26
		Re: Cannot understand a part of the IDL routine!! pls help!! By: Jeremy Bailin on Mon, 24 May 2010 05:16
		Re: Cannot understand a part of the IDL routine!! pls help!! By: David Fanning on Sun, 23 May 2010 09:07

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