[GRASS-dev] [GRASS GIS] #2098: i.vi gari wrong formula?

[GRASS GIS]

#2098: i.vi gari wrong formula?
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  Reporter:  kristinah    |       Owner:  grass-dev@…              
      Type:  defect       |      Status:  reopened                 
  Priority:  normal       |   Milestone:  7.0.0                    
 Component:  Imagery      |     Version:  svn-trunk                
Resolution:               |    Keywords:  i.vi                     
  Platform:  Unspecified  |         Cpu:  All                      
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Changes (by kristinah):

  * status:  closed => reopened
  * resolution:  fixed =>


Comment:

 Actually, the formula I provided was also wrong. The correct formula has
 the "+" in a different position

 GARI = ( nirchan - (greenchan- (bluechan - redchan))) /
 ( nirchan + (greenchan - (bluechan - redchan)))

 This was taken from the article where the formula was actually defined:
 Gitelson, Anatoly A.; Kaufman, Yoram J.; Merzlyak, Mark N. (1996)
 Use of a green channel in remote sensing of global vegetation from EOS-
 MODIS
 Remote Sensing of Environment 58 (3), 289-298.
 DOI: 10.1016/s0034-4257(96)00072-7

 When reading the explanation about the meaning of the index in this
 article, it became clear to me, that "indexdatabase.de" must be wrong.

 Sorry for pointing you in the wrong direction first!


 Replying to [ticket:2098 kristinah]:
 > The formula for GARI in the manual
 (http://grass.osgeo.org/grass70/manuals/i.vi.html) seems to be wrong. As
 it is now, the result would always be 1.
 >
 > It is
 > "
 > GARI = ( nirchan - (greenchan-(bluechan - redchan))) /
 > ( nirchan- (greenchan-(bluechan - redchan)))
 > "
 >
 > It should be (e.g. according to
 http://www.indexdatabase.de/db/i-single.php?id=363)
 > "
 > GARI = ( nirchan - (greenchan-(bluechan - redchan))) /
 > ( nirchan- (greenchan+(bluechan - redchan)))
 > "
 >
 > As the formula in the manual seems to be taken from code, the code might
 be wrong as well. I did not test the function, only read the manual
 online.

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Ticket URL: <http://trac.osgeo.org/grass/ticket/2098#comment:3>
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