Why does the raster calculator only give out 1 and 0 values?

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12-17-2018 05:46 AM
Lisa-MarieHille
New Contributor II

I have a problem with the raster calculator of ArcMap 10.5.1 because it only gives out a raster with 0 an 1 values. I'd like to calculate the Leaf Area Index out of a NDVI-Raster by using this equation:

LAI = (((1+NDVI)/(1-NDVI))*NDVI)^0.5

I already have a raster with the NDVI values ranging from approx. -0.699 to approx. 0.823. The Pixel type is floating point.

In the raster calculator I used the following expression:

(((1+"NDVI.img")/(1-"NDVI.img"))*"NDVI.img")^0.5

where "NDVI.img" is the raster file I named above. I looked at the graph of the equation and it should give out decimal values higher than 0, but I only get a raster file full of 0 and no stretched values. Can you tell me what I did wrong?

PS.: The output raster that gets created has the pixel type integer even if I set it to float beforehand.

#rastercalculator#float#integer#ndvi#leafareaindex

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5 Replies
XanderBakker
Esri Esteemed Contributor

Could you try to do this:

(((1.0 + "NDVI.img")/(1.0 - "NDVI.img")) * "NDVI.img")^0.5‍
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Lisa-MarieHille
New Contributor II

Thank you for your answer. I tried that but it didn't change the result.

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Lisa-MarieHille
New Contributor II

Another page could help me with the problem. So here is the solution if someone else has troubles like this: I used the operator ^ which is the "Boolean XOr operator" and it only returns 0 and 1 values. I wrote SquareRoot(...) around the equation instead and it worked just fine. 

EdisonParaiso
New Contributor

Your input raster may have a "Signed Integer" pixel type. If you want it to become float, add Float("your raster here") command on the raster calculator.

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Arthur_Morgan
New Contributor III

Do you know the reference of the LAI formula mentioned in your question?

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