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Re: Is there no NULL in IDL?? [message #30829]

Tue, 21 May 2002 10:29

Sean Raffuse
Messages: 46
Registered: July 2001

Member

"Wayne Landsman" <landsman@mpb.gsfc.nasa.gov> wrote in message
news:3CE97BDF.A7A1070B@mpb.gsfc.nasa.gov...
> Sean Raffuse wrote:
>
>> Am I just blind? What can I use for a null value when my data type is
>> integer? Please don't tell me zero.
>
> I can think of 4 options, each of which might be best in particular
> situations:
>
> (1) Use a known "non-physical" value (e.g. -32767) to flag nulls. (But
> be careful when applying numeric operations on the data .)
>
I would like to visualize the data using ENVI as a spectral profile. A
large negative value will give the same problem as a zero, only worse.

> (2) Convert to floating point and use NAN values to represent nulls.
>
Don't to convert to floats because the data is so large. I need to stick
with integers.

> (3) Carry around an extra byte mask array indicating which pixels are
> null.
>
This is a possibility, thanks for the help.

> (4) Carry around a "null pixel list" vector , i.e. a vector of 1-d
> indicies indicating which pixels in the data are null.
>
> --Wayne Landsman landsman@mpb.gsfc.nasa.gov
>

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[Message index]

		Re: Is there no NULL in IDL?? By: Sean Raffuse on Tue, 21 May 2002 10:29
		Re: Is there no NULL in IDL?? By: R.Bauer on Mon, 20 May 2002 23:10
		Re: Is there no NULL in IDL?? By: btupper on Mon, 20 May 2002 17:36
		Re: Is there no NULL in IDL?? By: Wayne Landsman on Mon, 20 May 2002 15:42

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