Ground Vegetation Index

[Bruce K. Wylie (303) 490 8336]

	NDVI is a value from -1 to 1. Often it is recoded to a
scaling from 1-255 to facilitate 8 bit files. Usually a linear
transfermation is used. Some only use the range of NDVI from -.1
to .6 and recode that from 1-255, thereby retaining more of the
NDVI information associated with biomass. Some recoding shemes
leave certian numbers out of the NDVI reclass numbers for
vectors or other overlays, e.g. 1-6 is for overlays and 7-255 is
NDVI or 1-250 is NDVI and 251-255 is for overlays.

Regards,


Bruce Wylie

> From: cis at terra.fct.unl.pt (Cristina Isabel Seabra [Ambiente])
> 
> 
> Hello GRASS users!
> 
> I've been trying to classify a LANDSAT TM image in terms of land use.
> I think it would be interesting to have a Ground Vegetation Index map and combine it with
> 2 other bands. I've used r.mapcalc to define the GVI. What I did was:
> GVI = (band4 - band3) / (band4 + band3) but the result I get is a map with only 2
> categories (-1 and 1). Shouldn't this GVI layer created by r.mapcalc have more
> information or am I doing something wrong when I write the expression in r.mapcalc?
> Is there someone that can help me in this matter?
> 
> Thanks,
> 
> Cristina Seabra
> New University of Lisbon
> Lisbon, Portugal
> 
> 
> cis at fct.unl.pt
> 
>