i.cluster

I am working with i.cluster and i.maxlik on multi-temporal GVI data for the former Soviet Union and I have some questions:

- Has anybody worked out a method of establishing the "natural" number of clusters that occur in multi-image data? Or a description of how changing the input parameters can change the results?
I have experimented with the input parameters that i.cluster asks for and I have some interesting results, however I would like to be able to justify my results with more than "it just looks better".

- In the class separability matrix its fairly obvious that small numbers indicate classes are closer than large numbers... but what are the units? When I specify a class separation of .7, what units am I using and can I use this matrix to compare the within class variation to the between class variation?

Thanks, Greg G.