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@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, Portugalcis@fct.unl.pt