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Re: NULL value in IDL ? [message #42321 is a reply to message #42320]

Wed, 02 February 2005 00:28

Jerome Colin
Messages: 8
Registered: February 2005

Junior Member

David Fanning wrote:
> Jerome Colin writes:
>> Is there in IDL a way to give a variable the value NULL, meaning 'no data' ?
>> My problem is that I use REBIN() to reduce an image, but some parts of
>> this image do not contain information, even is the value is zero. These
>> zero-value pixels are hence taken into account in the REBIN()
>> calculation, and that's what I would like to avoid.
>
> REBIN seems to work OK with NANs:
>
> a = findgen(5, 5)
> a[1,1] = !Values.F_NAN
> b = Rebin(a, 10, 10)
> print, b
>
> Cheers,
>
> David
>
Ok, now I replace values of the array with !values.f_NaN, it work properly.
But at the end, I use a WRITE_BMP() to have a look at the result. NaN
values cause a failure, so I tried to replace NaN values with 0. Has the
array dimensions have changed, I cannot use the index array I previoulsy
used :

search=WHERE(data le 0.) & data(search)=!values.f_NaN

And if I use :

search=WHERE(newdata eq !values.f_nan)

it returns -1.

What kind of operator can be used to identify NaN cells in my array ?

Many thanks, David !

Jerome

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[Message index]

		Re: NULL value in IDL ? By: K. Bowman on Wed, 02 February 2005 07:03
		Re: NULL value in IDL ? By: Jerome Colin on Wed, 02 February 2005 00:58
		Re: NULL value in IDL ? By: Jerome Colin on Wed, 02 February 2005 00:28
		Re: NULL value in IDL ? By: David Fanning on Tue, 01 February 2005 11:30

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