I think I know the answer to this. If so, it's a bug. i.vi operating on CELL maps produces integer output. Since most of these calculations produce results between 0 and 1, the result truncates to 0. Vegetation indices should be float, but input imagery maps are usually CELL. So this typically produces maps with all 0 values. i.vi should convert to float (the equivalent of multiplying by 1.0 in r.mapcalc).
Michael ____________________ C. Michael Barton Director, Center for Social Dynamics & Complexity Professor of Anthropology, School of Human Evolution & Social Change Arizona State University voice: 480-965-6262 (SHESC), 480-727-9746 (CSDC) fax: 480-965-7671 (SHESC), 480-727-0709 (CSDC) www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu On Oct 12, 2011, at 9:56 AM, Michael Barton wrote: > I just tried out the new i.vi in GRASS 7 and it doesn't seem to do anything. > > I've tested it with the landsat images in the NC07 demo data set. I set the > region to match the landsat images and ran: > > i.vi --overwrite viname=NDVI red=lsat7_2000_30@landsat > nir=lsat7_2000_40@landsat green=lsat7_2000_20@landsat > blue=lsat7_2000_10@landsat chan5=lsat7_2000_50@landsat > chan7=lsat7_2000_70@landsat output=GEMI_lsat7_2000 > > I get a map with all 0's > > I got the same result with the GEMI and NDVI routines. Am I doing something > wrong or is this a bug. > > Michael > ____________________ > C. Michael Barton > Director, Center for Social Dynamics & Complexity > Professor of Anthropology, School of Human Evolution & Social Change > Arizona State University > > voice: 480-965-6262 (SHESC), 480-727-9746 (CSDC) > fax: 480-965-7671 (SHESC), 480-727-0709 (CSDC) > www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu > > > > > > > > > > >
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