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

[Gökçen Güner]

Hi,
We did both statistics calculation using QGis because ERDAS couldn't
calculate statistics for Grass output (or we couldn't do it). I'm sure that
Grass output is floating point map but I'll check Erdas one.
Thanks

2013/1/14 Angelos Tzotsos <gcpp.kalxas at gmail.com>

>  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)
>
>
>
>
> _______________________________________________
> grass-user mailing listgrass-user at lists.osgeo.orghttp://lists.osgeo.org/mailman/listinfo/grass-user
>
>
> 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 Athenshttp://users.ntua.gr/tzotsos
>
>
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