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Re: NULL value in IDL ? [message #42320 is a reply to message #42317]

Wed, 02 February 2005 00:58

Jerome Colin
Messages: 8
Registered: February 2005

Junior Member

Jerome Colin wrote:
> 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
Oups... Forget my question, I've found your answer on your web site, in
math tips 'finding NaN in arrays'.
Thank you for your help.
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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