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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