[GRASS-user] Re: algorithm used in i.cluster
Georg Kaspar
georg at muenster.de
Thu Apr 22 07:59:06 EDT 2010
Markus Neteler wrote:
> Luckily it is open source :)
and also quite well documented (at least it is possible to understand
what's going on without being a C-guru)
>> does anybody know which exact algorithm is used (k-means probably...)?
>
> I'm afraid that you need to compare it to a k-means algorithm. Please let
> us know your findings.
the steps described in
http://download.osgeo.org/grass/grass6_progman/c__exec_8c_source.html
seem to fit the migrating means algorithm described in richards and jia
(2006) and based on the isodata algorithm in ball and hall (1965):
1. set C initial cluster centers (at random)
2. assign each pixel to the nearest center
3. compute a new set of means
4. repeat until no further changes occur. (shapiro also implemented a
maximum number of iterations)
empty clusters can also be deleted and similar clusters can be merged as
implemented in i.cluster.
best regards,
Georg
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