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Re: Rescaling byte (0-200) ndvi to -1 to 1 values [message #80868 is a reply to message #80863]

Thu, 19 July 2012 11:41

Paul Van Delst[1]
Messages: 1157
Registered: April 2002

Senior Member

On 07/19/12 14:18, Narnia wrote:
> I'm using the eMODIS 10-day product from the USGS with this description: "MODIS NDVI data are stretched (mapped)
> linearly (to byte values) as follows: [-1.0, 1.0] -> [0, 200] Invalid Values: 201 - 255
>
> NDVI = (value ï¿½ 100) / 100; example: [ (150 ï¿½ 100) / 100 = 0.5 NDVI ]"
>
> I am trying thus to scale the data in ENVI just using Band Math [expression:((b1-100)/100)] and all the values I get
> are 0 across my entire image. Any thoughts as to why?

IDL> value = 150
IDL> help, (value - 100) / 100
<Expression> LONG = 0

IDL> value = 150.0
IDL> help, (value - 100) / 100
<Expression> FLOAT = 0.500000

>
> Secondly, I need to do this for over 400 images; can someone suggest a quick script that can read and scale this data
> in IDL? I tried 'ScaledImage' but i keep getting errors as well...

I would write one myself. Mostly since the scaling is just a one-line operation. At least you know you're getting the
correct (or wrong) answer that way. :o)

cheers,

paulv

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[Message index]

		Re: Rescaling byte (0-200) ndvi to -1 to 1 values By: Narnia on Fri, 20 July 2012 07:01
		Re: Rescaling byte (0-200) ndvi to -1 to 1 values By: Narnia on Fri, 20 July 2012 07:05
		Re: Rescaling byte (0-200) ndvi to -1 to 1 values By: David Fanning on Fri, 20 July 2012 06:07
		Re: Rescaling byte (0-200) ndvi to -1 to 1 values By: Narnia on Fri, 20 July 2012 06:03
		Re: Rescaling byte (0-200) ndvi to -1 to 1 values By: Paul Van Delst[1] on Thu, 19 July 2012 13:13
		Re: Rescaling byte (0-200) ndvi to -1 to 1 values By: Narnia on Thu, 19 July 2012 12:19
		Re: Rescaling byte (0-200) ndvi to -1 to 1 values By: Paul Van Delst[1] on Thu, 19 July 2012 11:41
		Re: Rescaling byte (0-200) ndvi to -1 to 1 values By: k.shemsu on Mon, 20 May 2013 05:39

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