faster calculation for Distance in Meters between two points on earth - Android android.location

Android examples for android.location:Distance

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Description

faster calculation for Distance in Meters between two points on earth

Demo Code

public class Main {

  private static final double EARTH_RADIUS_METERS = 6367000.0;
  private static final double RAD_PER_DEG = Math.PI / 180.0;

  public static double fastDistanceMeters(double latRad1, double lngRad1, double latRad2, double lngRad2) {
    if ((Math.abs(latRad1 - latRad2) > RAD_PER_DEG) || (Math.abs(lngRad1 - lngRad2) > RAD_PER_DEG)) {
      return accurateDistanceMeters(latRad1, lngRad1, latRad2, lngRad2);
    }/*w  w  w  .  j a v a2  s .c  om*/
    // Approximate sin(x) = x.
    double sineLat = (latRad1 - latRad2);

    // Approximate sin(x) = x.
    double sineLng = (lngRad1 - lngRad2);

    // Approximate cos(lat1) * cos(lat2) using
    // cos((lat1 + lat2)/2) ^ 2
    double cosTerms = Math.cos((latRad1 + latRad2) / 2.0);
    cosTerms = cosTerms * cosTerms;
    double trigTerm = sineLat * sineLat + cosTerms * sineLng * sineLng;
    trigTerm = Math.sqrt(trigTerm);

    // Approximate arcsin(x) = x
    return EARTH_RADIUS_METERS * trigTerm;
  }

  public static double accurateDistanceMeters(double lat1, double lng1, double lat2, double lng2) {
    double dlat = Math.sin(0.5 * (lat2 - lat1));
    double dlng = Math.sin(0.5 * (lng2 - lng1));
    double x = dlat * dlat + dlng * dlng * Math.cos(lat1) * Math.cos(lat2);
    return (2 * Math.atan2(Math.sqrt(x), Math.sqrt(Math.max(0.0, 1.0 - x)))) * EARTH_RADIUS_METERS;
  }

}

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