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From Neil Ireson <N.Ire...@dcs.shef.ac.uk>
Subject Using GeohashPrefixTree for map clustering
Date Thu, 13 Dec 2012 19:43:25 GMT
Hi,

I would like to be able to display up to multiple millions of lat/lng  
points on a map, to make this possible my intention is to plot less  
than 1000 clusters of points by dividing the world into a grid tree  
and I'm looking into using GeohashPrefixTree to do this.

I am imagining that I would index each of the levels generated by  
GeohashPrefixTree in a separate field (e.g. geo_level_0, geo_level_1,  
etc.)

I would use the current viewport on the map as the bounding box to  
select the documents to display, and then use the map zoom level to  
select the appropriate geo_level field to use for clustering.

The other this I'm unclear about is how to convert the values in the  
geo_level fields back into lat/lng. If I take the centre of each grid  
represented by the level values are these constant points on the  
earth? The other, more visually pleasing, approach would be to  
calculate the weighted average of points in each grid, although this  
will obviously entail maintaining a three values for each grid (i.e.  
total lat, total lon, number of points).

So my questions are

1) Does this sound like a sane idea (obviously hoping I've explained  
it well enough)?

2) Has anyone done something similar and could they can share issues  
encountered, enlightenment gained, code?

thanks

N


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