[GRASS-user] Differences Between ERDAS and GRASS About NDVI Statistics

[Angelos Tzotsos]

On 01/14/2013 01:03 AM, Gökçen Güner wrote:
> Hi,
> This will not be a specific GRASS question. My friend and I tried to
> calculate NDVIs of same data set and results seem same to us. But checking
> statistics of each output we saw that statistics are very different. I
> mean, median, mean, std.dev values of Grass output and Erdas output are
> different. We couldn't find an explanation for this situation. What can be
> the reason for this?
>
> PS:
> For NDVI, we used this formula: (NIR_Band - RED_Band) / (NIR_Band +
> RED_Band)
>
>
>
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Hi,

Please make sure that the output images are of the same type in both 
cases and that your statistic calculation method is the same.
NDVI is a float (or double) result if your initial data are integers 
(usually they are).
Perhaps one of your images is automatically converted to 8 bit integer type?

Cheers,
Angelos

-- 
Angelos Tzotsos
Remote Sensing Laboratory
National Technical University of Athens
http://users.ntua.gr/tzotsos

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