ELKI DBSCAN LngLatDistanceFunction producing one cluster -

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i'm using elki lnglatdistancefunction cluster lon/lat points it's returning 1 cluster (was returning more clusters when used euclid distance). tried multiple epsilon values i'm still getting 1 cluster.

    int minpts=20;     double eps=10;     listparameterization params = new listparameterization();     params.addparameter(dbscan.distance_function_id, lnglatdistancefunction.class);     params.addparameter(dbscan.parameterizer.minpts_id, minpts);     params.addparameter(dbscan.parameterizer.epsilon_id, eps);      params.addparameter(abstractdatabase.parameterizer.database_connection_id, dbcon);     params.addparameter(abstractdatabase.parameterizer.index_id, rstartreefactory.class);     params.addparameter(rstartreefactory.parameterizer.bulk_split_id, sorttilerecursivebulksplit.class);     params.addparameter(abstractpagefilefactory.parameterizer.page_size_id, 600);      database db = classgenericsutil.parameterizeorabort(staticarraydatabase.class, params);     db.initialize();      generalizeddbscan dbscan = classgenericsutil.parameterizeorabort(generalizeddbscan.class, params);

the distance in meters. therefore, need choose epsilon such - not points - have more minpts neighbors.

you can use knndistancessampler class estimate parameter. not automatic estimation. can plot resuling distances, , check "knee" in plot.

pay attention "noise" flag.

  • if single cluster, , "noise", epsilon small.
  • if single cluster, , "cluster" (not noise), epsilon large.
  • if single cluster, , "noise", minpts may large.
  • if single cluster, , cluster, minpts may small.

for applications, easier fix minpts 4, or 10, or 20; , adjust epsilon parameter desired. geographic applications yours, may easier fix epsilon parameter, , vary minpts parameter instead. example, may know distance of less 10000 meter indicates objects "neighbors".

algorithms such optics helpful choose parameter visually. (use minigui!)


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