[GRASS-user] r.kappa query

[daniel mcinerney]

Hi list,

I have a query regarding the error matrix produced
using r.kappa (in GRASS 6.4.0 RC6) and hoping that
the following will help someone to replicate my findings.
>From what I see, the error matrix is mis-labeling the
rows/columns in the matrix.

Using the spearfish dataset, I digitised 18 points
to create a reference dataset to validate
the classification, in this case the raster 'landcover.orig'
For the purposes of the test and simplicity, I ensured
that the points  were located within two landcover classes
(raster values 42 and 81). The following steps were carried out
to generate the output from r.kappa


#Create reference dataset
d.where | r.what input=landcover.orig > kappa_test.txt

For the purposes of this test, I deliberately changed the
landcover class from 42 to 32 in the validation dataset [1]
This will create an off-diagonal value in the error matrix.

#Create the vector point from ascii and convert to raster
v.in.ascii input=kappa_test output=kapp_test cat=4
v.to.rast input=kapp_test output=validation use=cat

#Run r.kappa
r.kappa classification=landcover.orig reference=validation
output=validation.txt

The output from r.kappa  (validation.txt) is below, however, it appears
to me that the matrix is transposed, i.e. the horizontal values
(MAP1) should in fact be vertical. From my interpretation, the error
matrix indicates that 8 validation points with the value 42 were
classified as 32, but in fact it should state that 8 points with
the value of 32 were classified as 42? Can anyone confirm
my findings?

Thanks in advance.

Regards,
Daniel.


                        ACCURACY ASSESSMENT
LOCATION: spearfish60                           Fri Apr  1 12:45:42 2011
MASK: none
MAPS: MAP1 = Categories (validation in user1)
      MAP2 = (untitled) (landcover.orig in PERMANENT)

Error Matrix
Panel #1 of 1
                          MAP1
     cat#       32      42      81      Row Sum
 M    32        0       8       0       8
 A    42        0       0       0       0
 P    81        0       0       10      10
Col Sum         0       8       10      18


Cats    % Commission    % Ommission     Estimated Kappa
32      100.000000      -nan    -999.000000
42      NA              NA              NA
81      0.000000        0.000000        1.000000

Kappa           Kappa Variance
0.357143        0.002343

Obs Correct     Total Obs       % Observed Correct
10              18              55.555556



[1]
#validation input
590188.6875|4919453.8125||32
590188.6875|4918947||32
590307.9375|4918350.75||32
590576.25|4917694.875||32
590307.9375|4917694.875||32
590546.4375|4919364.375||32
590874.375|4919364.375||32
590904.1875|4919483.625||32
603604.3125|4922047.5||81
603336|4922315.8125||81
603514.875|4922464.875||81
603604.3125|4922256.1875||81
603634.125|4922107.125||81
603693.75|4921987.875||81
603962.0625|4921987.875||81
603753.375|4921600.3125||81
603962.0625|4922047.5||81
598983.375|4922256.1875||81
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.osgeo.org/pipermail/grass-user/attachments/20110401/06f2e405/attachment.html