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

[Markus Metz]

Feeding the test values and the evi(2) formula to r.mapcalc, the
results are more or less in the expected range, still beyond [-1, 1],
but not much. Obviously, there is a bug in i.vi. Furthermore, i.vi is
slower than r.mapcalc. I recommend to replace the C module i.vi with a
i.vi script that calls r.mapcalc.

Markus M


On Sun, Jun 16, 2013 at 8:13 PM, Nikos Alexandris
<nik at nikosalexandris.net> wrote:
> 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
> _______________________________________________
> grass-dev mailing list
> grass-dev at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/grass-dev