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Re: Changing values of one image from ENVI [message #62313 is a reply to message #62270]

Sun, 31 August 2008 17:07

jeffnettles4870
Messages: 111
Registered: October 2006

Senior Member

On Aug 31, 2:37 pm, Jonathan Greenberg <jgrn...@gmail.com> wrote:
> Again, the question is do you need to use a full image to do spatial
> analysis? There are *some* analyses that really require in the entire
> image, but local neighborhood spatial analyses are not one of the ones
> that need ENVI_GET_DATA -- its much more scalable to simply pull a set
> of lines using ENVI_GET_SLICE the size of your window into an array
> rather than running on the entire dataset. If you have the memory and
> small enough images, ENVI_GET_DATA can work fine, but with increasing
> image sizes (I routinely work with images that range from 1gb to
> 100gb), I come across a lot of code that does not scale because of
> that one command, when it only takes a few more lines of code to
> perform tiled analyses.
>
> Is the overhead incurred by repeated use of ENVI_GET_SLICE vs.
> ENVI_GET_DATA significant as compared to the total time of processing
> an image (assuming memory issues are not an issue)? Has anyone done
> any tests on this?
>
> --j

I think the point is that ENVI routines give you many different ways
to access your data, and the best choice of which to use depends on
what you want to do with the data. I often think of ENVI_GET_SLICE
and ENVI_GET_DATA routines as tiling routines that just return a
single tile :) If you simply want to read in a few pixels, do it -
you have that ability using either ENVI_GET_SLICE or ASSOC(). Or, as
Chris pointed out, you can POINT_LUN to whatever you need to get to.
I use these routines in different situations all the time. The real
issues here are the format of your data and what you're trying to do
with those data. If you were, for example, trying to just operate on
band 1 of an image cube, why would you bother with ENVI_GET_SLICE?
ENVI_GET_DATA seems much simpler to me in that case.

Jeff

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[Message index]

		Changing values of one image from ENVI By: txominhermos on Fri, 29 August 2008 08:20
		Re: Changing values of one image from ENVI By: Chris Jengo on Sun, 31 August 2008 21:56
		Re: Changing values of one image from ENVI By: txominhermos on Mon, 15 September 2008 02:23
		Re: Changing values of one image from ENVI By: jeffnettles4870 on Sun, 31 August 2008 17:07
		Re: Changing values of one image from ENVI By: Jonathan Greenberg on Sun, 31 August 2008 11:37
		Re: Changing values of one image from ENVI By: Chris Jengo on Sun, 31 August 2008 07:25
		Re: Changing values of one image from ENVI By: Chris Jengo on Sun, 31 August 2008 07:07

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