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February 9th, 2008, 04:51 PM  #1 
Joined: Feb 2008 Posts: 1  Finding clusters of points on a grid
I need to find clusters of points on a grid 2000.00*2000.00 (2 d.p. accuracy). Specifically, i need to find the cluster which has the most points in the smallest area. The number of points is arbitrary, and the algorithm needs to be as fast as possible. Please help.

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February 9th, 2008, 08:53 PM  #2 
Joined: Dec 2007 Posts: 138  Re: Finding clusters of points on a grid
# of points is arbitrary, and pseudorandom? Isn't that problem NPComplete? 
February 10th, 2008, 06:09 PM  #3 
Joined: Dec 2007 Posts: 232  Re: Finding clusters of points on a grid
We need to know more. To solve the problem at all (regardless of efficiency) we need to know what "the most points in the smallest area" means. If you can choose any area you want, it would be just large enough to fit a single point, right? Otherwise you must have limitations on the size and shape of the area, and we need to know this. Second, if you want this to be efficient: * Are approximate answers acceptable, or not? For dense collections of points an approximate answer might be a thousand times faster. * How many points are there? If there are ten points in a 200000x200000 grid, then the optimal method will likely go pointbypoint; if you have a billion points, probably not. If this scales from 1 point to 40 billion points, then it's dense 'on average' so a dense method is probably best. 

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clusters, finding, grid, points 
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