[GRASS-user] NDVI from landsat 5 TM

[Hamish]

stephen sefick wrote:
> I would like to calculate NDVI and
> EVI from ladsat 5 data.  The data
> is scaled 0-255.  Do I need to convert this to
> watts/meter sqaured
> before I proceed?  I have done this calculation
> (band4-band3)/(band5+band3) and get a map filled with
> zeros.  What am I doing wrong.


maybe it is integer division resulting in a integer result?


try  (1.0*band4-band3)/(band5+band3)  to introduce a floating
point value and so get a floating point result.


Hamish