[mapserver-dev] MS RFC 69 - Call for vote
szekerest at gmail.com
Thu Mar 3 04:48:05 EST 2011
2011/3/3 Lime, Steve D (DNR) <Steve.Lime at state.mn.us>
> Pretty friggin’ cool. Takes a minute to get ones head around what’s going
> on. Is this interpretation correct?
> - Grey box indicates a cluster representing multiple types
> - Icon with a number indicates a cluster representing a single
> - Blue dots are the points being clustered
Yes, that was my intention what you mentioned. The displayed image is
controlled by a single (aggregated) attribute 'zoomcode' provided by the
data source (see the corresponding
mapfile<http://vbkto.dyndns.org/cgi-bin/cluster.map>for the details).
But this configuration is highly customizable. For example
you can define a group expression (which evaluates to a string value) to
define which shapes should be considered to belong to the same group at all.
This group value is also exposed as an attribute (Cluster:Group) which can
also be used for classification/labeling.
Another powerful option is to define a filter expression which evaluates to
a boolean value and defines whether the current shape should be added to a
group or not. By using this, you may exclude certain shapes to take part in
the clustering, or you may define a filter expression like:
"([Cluster:FeatureCount]<20)" to limit the number of the features for each
The greatest challenge with the clustering is to select the most feasible
rank expression by using a reasonable combination of the position offset,
variance and the feature count. This rank expression determines which
tentative clusters are selected and added to the list of the finalized
clusters. We may probably expose some weighting coefficients for the user to
provide better control on this.
I agree that a good documentation will also be required to enumerate all
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