Best algorithm for comparing a base coordinate with a list of n coordinates and determining the nearest m coordinates?

Question

I have code doing this right now. It works great with small and medium lists, but when I have a list of size n> 5000, my algorithm can take almost 1 minute on a mobile device. I mainly compare the Coordinate object in Java with the list of (Vector) Coordinate objects.

Here is my basic algorithm:

• move each item in nx list
• if the list of “10 closest” has less than 10 elements, add nx to the list and go to the next element
• if there are already 10 elements in the "10 closest" list, then calculate the distance between nx and the base Coordinates
• if the distance is less than the farthest distance in the "10 closest list", then remove the most distant element from this list and replace it with nx

I keep looking at it and trying to find a more efficient way to do it. This seems like a sort algorithm problem, so there should be a better way.

Here is my distance calculation method:

public static double distance(double lat1, double lon1, double lat2, double lon2, char unit) {

  double theta = lon1 - lon2;

  double dist = Math.sin(deg2rad(lat1)) * Math.sin(deg2rad(lat2)) + Math.cos(deg2rad(lat1)) * Math.cos(deg2rad(lat2)) * Math.cos(deg2rad(theta));

  dist = acos(dist);

  dist = rad2deg(dist);

  dist = dist * 60 * 1.1515;

  if (unit == 'K') {

    dist = dist * 1.609344;

  } else if (unit == 'N') {

    dist = dist * 0.8684;

    }

  return (dist);

}

Answer 1

You can save your coordinates in some tree of space splitting .

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Answer 2

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Answer 3

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