Question

I have a table in MySQL db which two of it’s columns are the latitude and the longitude of a given geo-point. it’s defined as Float(2,6).
I want to select only the records within a specific radius from a given point.

I found the following code in Java, that checks the distance between to geo-points:

public class Location {

private int latitudeE6;
private int longitudeE6;
    ...
}

public static double CalculateDistance(Location StartP, Location EndP) {

      double lat1 = StartP.getLatitudeE6()/1E6;
      double lat2 = EndP.getLatitudeE6()/1E6; 
      double lon1 = StartP.getLongitudeE6()/1E6;     
      double lon2 = EndP.getLongitudeE6()/1E6;
      double dLat = Math.toRadians(lat2-lat1); 
      double dLon = Math.toRadians(lon2-lon1);   
      double a = Math.sin(dLat/2) * Math.sin(dLat/2) + 
      Math.cos(Math.toRadians(lat1)) * Math.cos(Math.toRadians(lat2)) *
      Math.sin(dLon/2) * Math.sin(dLon/2); 
      double c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
      return earthradius * c;
   }

Currently, I’m doing SELECT without the location, and then I go over the result set and checks if it’s in the radius given. (in Java).
This is surely not the most elegant, efficient way of doing it.
Can you think of a better way ?

Answer 1

Here’s a presentation that describes (I think) how to do what you’re attempting to accomplish in MySQL: Geo/Spatial Search with MySQL