[email protected] wrote: Didrik: > >> I don't know if this is interesting for you but this postgis thread was >> related to the subject of your mail : >> >> http://postgis.refractions.net/pipermail/postgis-users/2005-July/008642.html
Interesting, but as one of the replies said, the clustering algorithm is iterative in nature, which is hard to do in a SQL query. Yves: > > That series of posts is about statistical data clustering as in k-means > and the like. Give a k-means like algorithm a number of seeds N, it > will minimize some sum of squares of distances between those seed points > and the data points and your N clusters will be produced. > > That's not how the clustering strategy in OL is implemented AFAIK. Come > to think of it a pregenerated set of clusters could be done on distance > to seed points (e.g. know site locations ?), but that would need to be > done for every zoom level and even every "tile" in a given zoom level. Yes, definitely. For my needs I have come up with this: * A separate table for the cluster features, with columns for the geometry (a point), a feature count and the scale (i.e. I store the cluster points for all scales in one table) * A view for each scale "create view cluster_1M as select * from clusters where scale = 1000000" etc. * A stored procedure which runs the same clustering algorithm as OpenLayers.Strategy.Cluster on the original spatial table and adds the clusters in the cluster table. * Then I'll set up the layers and scale limits so that the cluster layer for each scale is dispalyed for that scale only. * I'll probably add a trigger on the original spatial table and add each single new point to the clusters rather than have to regenerate the whole thing. The backend is Oracle Spatial (10.2). -- Nils Weinander | Systems Designer Phone +46 (0)8 4100 6456 Mobile +46 (0)709 78 28 37 -- Curalia AB | www.curalia.se Hudiksvallsgatan 4, 113 30 Stockholm, Sweden -- _______________________________________________ Users mailing list [email protected] http://openlayers.org/mailman/listinfo/users
