[GRASS-dev] Unexpected EVI range from "i.vi"

[Nikos Alexandris]

Nikos Alexandris wrote:
> > > I get an unexpected range of evi values using "i.vi" (G7), i.e.

[..]

> > > 	# range is...
> > > 	r.info -r evi

> > > 	min=-6912.82161611806
> > > 	max=2264.42037461018

[..]

> Looking for these pixels, e.g.
> 
> 	r.stats evi_ToAR -g | grep '\-5905'
> 
> 	784935 2695215 -5905.4417191748
> 	786465 2694675 -5905.4417191748
> 	766185 2685615 -5905.4417191748
> 
> and
> 
> 	r.stats evi_ToAR -g | grep '6952\.'
> 
> 	783435 2690025 6952.8054373157



> Then tracing the values that produced this out-of-range value,
> 
> 	r.what coordinates=784935,2695215
> map=B.Trimmed.ToAR.1,B.Trimmed.ToAR.3,B.Trimmed.ToAR.4,evi_DN,evi_ToAR
> 
> 	784935|2695215||0.230260364323039|0.110923862670943|0.0614305088322746|
> 0.35181236673774|-5905.44171917482
> 
> and
> 
> 	r.what coordinates=783435,2690025
> map=B.Trimmed.ToAR.1,B.Trimmed.ToAR.3,B.Trimmed.ToAR.4,evi_DN,evi_ToAR
> 
> 	783435|2690025||0.228143006540123|0.106632395012542|0.0712654621906476|
> 0.296610169491526|6952.80543731566



A bit more clear perhaps:

# res=30
g.region -pagc rast=B.Trimmed.ToAR.1 res=30

n=2815500
s=2621340
w=658560
e=875880
nsres=30
ewres=30
rows=6472
cols=7244
cells=46883168
center_easting=767220.000000
center_northing=2718420.000000

# what is there?
r.what coordinates=784935,2695215 
map=B.Trimmed.ToAR.1,B.Trimmed.ToAR.3,B.Trimmed.ToAR.4,evi_DN,evi_ToAR

784935|2695215||0.230260364323039|0.110923862670943|0.0614305088322746|
0.35181236673774|-5905.44171917482

# while res=1...
g.region -pagc rast=B.Trimmed.ToAR.1 res=1

n=2815500
s=2621340
w=658560
e=875880
nsres=1
ewres=1
rows=194160
cols=217320
cells=42194851200
center_easting=767220.000000
center_northing=2718420.000000

# ...gives
r.what coordinates=784935,2695215 
map=B.Trimmed.ToAR.1,B.Trimmed.ToAR.3,B.Trimmed.ToAR.4,evi_DN,evi_ToAR

784935|2695215||0.230260364323039|0.110923862670943|0.0614305088322746|
0.35181236673774|-5905.44171917482



Now, "pointing" to the suspect pixel:

# both res=30  &  res=1 give the same result, of course
g.region -pagc e=784935 n=2695215 rows=1 cols=1 res=30

n=2695230
s=2621340
w=658560
e=784950
nsres=73890
ewres=126390
rows=1
cols=1
cells=1
center_easting=721755.000000
center_northing=2658285.000000

# what is there?
r.what coordinates=784935,2695215 
map=B.Trimmed.ToAR.1,B.Trimmed.ToAR.3,B.Trimmed.ToAR.4,evi_DN,evi_ToAR

784935|2695215||0.264138088849702|0.372703389833447|
0.438437054236573|-0.203045685279188|0.0970312073830427

[..]

I guess it has to do with the extent/res definitions...

Thanks, Nikos