[GRASS-user] Signature file structure

GRASS GRASS user
1

Hi everyone

I have runned i.gensig and I would like to know where can I find some information regarding the strucutre of the file? Just to know which value refers to what
Thanks

Pedro

2

Pedro Roma wrote:

I have runned i.gensig and I would like to know where can I find some
information regarding the strucutre of the file? Just to know which value
refers to what

From the "g.manual i.gensig":

"...the resultant signature file (containing the means and covariance
matrices) for each class in the training map..."

Perhaps just reading the created signature (text) files and identifying the
mean's and variance/covariance matrices is enough.

Nikos

3

On Wednesday 28 of July 2010 21:22:08 Nikos Alexandris wrote:

Perhaps just reading the created signature (text) files and identifying
the mean's and variance/covariance matrices is enough.

Didn't have a look yet but the "Mean's ... matrices" is I guess wrong. The
signature file probably contains mean values (one mean value for each training
class) and the var./covar. matrices (one matrix for each training class).

Nikos

4

Ok as far as I can see it’s
Category ID (class)
Mean vector (each value is the average for the category in each band)

Var(b1;b1)
Cov(b1,b2) Var(b2;b2)
Cov(b1,b3) Cov(b2,b3) Var(v3,v3)

it’s this?
By the way, is in any place the inversion of the covariance matrix?

Thanks
Pedro

On Wed, Jul 28, 2010 at 8:30 PM, Nikos Alexandris <nikos.alexandris@felis.uni-freiburg.de> wrote:

On Wednesday 28 of July 2010 21:22:08 Nikos Alexandris wrote:

Perhaps just reading the created signature (text) files and identifying
the mean’s and variance/covariance matrices is enough.

Didn’t have a look yet but the “Mean’s … matrices” is I guess wrong. The
signature file probably contains mean values (one mean value for each training
class) and the var./covar. matrices (one matrix for each training class).

Nikos

5

Pedro:

Ok as far as I can see it's
Category ID (class)
Mean vector (each value is the average for the category in each band)

Var(b1;b1)
Cov(b1,b2) Var(b2;b2)
Cov(b1,b3) Cov(b2,b3) Var(v3,v3)

it's this?

It would take me to perform a test with numbers and see what is what exactly.
Maybe some math-grass-guru can explain quickly :wink:

By the way, is in any place the inversion of the covariance matrix?

Hmm... are you looking for this (or relevant):
<http://trac.osgeo.org/grass/browser/grass/branches/releasebranch_6_4/imagery/i.gensig/check.c&gt;

Nikos

ps: Maybe we can put this in the wiki after it is clear what is what