…say to cluster points in a map based on the zoom?
(information about the GVM Java library)
I was just asked this question by email, and thought I’d respond via a blog post in case the same query recurs. This short answer is: I certainly hope so, it’s exactly the kind of task the library was designed for, but there are some caveats:
I’ve not personally used the library on Android - there could be some minor incompatibilities due mismatches between the standard Java APIs and Android (though I don’t anticipate any). Should such an issue arise, I’m sure it could be patched very quickly.
As standard, I would typically use the implementation in the com.tomgibara.cluster.gvm.dbl package that uses double coordinates. But since double arithmetic may perform really poorly on handsets (I don’t know) it may be necessary to use alternative coordinate types for better performance (the float based com.tomgibara.cluster.gvm.flt for example). Note that whatever primitive coordinate-type you use, it will not avoid all double arithmetic.
How many points do you have device side? Making point clustering worthwhile when panning and zooming freely around a map implies to me that there are lots of points. A natural question is how do these points find their way into the application in the first place? Downloading 1M points in response to a query and then clustering them into 30 groups for display is probably not a good use of the device’s resources. Of course GVM could be used server side too, to provide a quick result to the user while lots more results streamed in for clustering in near-real-time.
Finally, I’d add the comment that GVM is very well suited to exactly this sort of application because of the flexibility that it provides around cluster keys: each time a cluster is enlarged or merged, the application is given the opportunity to modify the key - this means that the cluster key can be used to maintain all the salient state for the application (and no more, so performance can remain good).
In this online demonstration the cluster is keyed against the most populous city in the cluster but this could easily have been something else entirely.
tomgibara posted this
