Re: Best way to...

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  • Posted by irv Oct 17, 2010
  • 1793 views

Might be a bit more to it than that: for example, Montreal and Venice, IT are at almost the same latitude, but nowhere near close to each other in longitude.

So it could well turn out that the 3 closest (or the n closest) in one coordinate might not have any overlap with the 3 (or n) closest in the other coordinate.

How big is n?

The formula for computing distance between 2 points: 

d=2*asin(sqrt((sin((lat1-lat2)/2))^2 +  
                 cos(lat1)*cos(lat2)*(sin((lon1-lon2)/2))^2))

I could compute all 25k distances, but perhaps there's an easier way? Hashing lat/lon perhaps?

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