[GRASS-dev] question about i.vi

GRASS GIS GRASS GIS developer
1

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

2

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