/// <summary>
/// Calculate the distance between two points. This algorithm does not take the curvature of the Earth into
/// account, so it only works for small distance up to, say 200 km, and not too close to the poles.
/// </summary>
/// <param name="p1">Point 1. @Nonnull</param>
/// <param name="p2">Point 2. @Nonnull</param>
/// <returns>Straight distance between p1 and p2. Only accurate for small distances up to 200 km.</returns>
public static double distanceInMeters(Point p1, Point p2)
{
CheckArgs.checkNonnull("p1", p1);
CheckArgs.checkNonnull("p2", p2);
Point from;
Point to;
if (p1.lonDeg <= p2.lonDeg)
{
from = p1;
to = p2;
}
else
{
from = p2;
to = p1;
}
// Calculate mid point of 2 latitudes.
double avgLat = from.latDeg + ((to.latDeg - from.latDeg) / 2.0);
double deltaLonDeg360 = Math.Abs(to.lonDeg - from.lonDeg);
double deltaLonDeg = ((deltaLonDeg360 <= 180.0) ? deltaLonDeg360 : (360.0 - deltaLonDeg360));
double deltaLatDeg = Math.Abs(to.latDeg - from.latDeg);
// Meters per longitude is fixed; per latitude requires * cos(avg(lat)).
double deltaXMeters = degreesLonToMetersAtLat(deltaLonDeg, avgLat);
double deltaYMeters = degreesLatToMeters(deltaLatDeg);
// Calculate length through Earth. This is an approximation, but works fine for short distances.
double lenMeters = Math.Sqrt((deltaXMeters * deltaXMeters) + (deltaYMeters * deltaYMeters));
return(lenMeters);
}
/// <summary>
/// Create a random point, uniformly distributed over the surface of the Earth.
/// </summary>
/// <param name="randomGenerator">Random generator used to create a point. @Nonnull</param>
/// <returns>Random point with uniform distribution over the sphere. @Nonnull</returns>
public static Point fromUniformlyDistributedRandomPoints(Random randomGenerator)
{
CheckArgs.checkNonnull("randomGenerator", randomGenerator);
// Calculate uniformly distributed 3D point on sphere (radius = 1.0):
// http://mathproofs.blogspot.co.il/2005/04/uniform-random-distribution-on-sphere.html
double unitRand1 = randomGenerator.NextDouble();
double unitRand2 = randomGenerator.NextDouble();
double theta0 = (2.0 * Math.PI) * unitRand1;
double theta1 = Math.Acos(1.0 - (2.0 * unitRand2));
double x = Math.Sin(theta0) * Math.Sin(theta1);
double y = Math.Cos(theta0) * Math.Sin(theta1);
double z = Math.Cos(theta1);
// Convert Carthesian 3D point into lat/lon (radius = 1.0):
// http://stackoverflow.com/questions/1185408/converting-from-longitude-latitude-to-cartesian-coordinates
double latRad = Math.Asin(z);
double lonRad = Math.Atan2(y, x);
// Convert radians to degrees.
System.Diagnostics.Debug.Assert(!Double.IsNaN(latRad));
System.Diagnostics.Debug.Assert(!Double.IsNaN(lonRad));
double lat = RadianToDegree(latRad);
double lon = RadianToDegree(lonRad);
return(fromMicroDeg(degToMicroDeg(lat), degToMicroDeg(lon)));
}
