public double SphericalDistance(Coords me, Coords item)
{
double degreesToRadians = Math.PI / 180.0;
// phi = 90deg - latitude
double mePhi = (90.0 - me.Latitude) * degreesToRadians;
double itemPhi = (90.0 - item.Latitude) * degreesToRadians;
// theta = longitude
double meTheta = me.Longitude * degreesToRadians;
double itemTheta = item.Longitude * degreesToRadians;
// Compute spherical distance from spherical coordinates
// For two locations in spherical coordinates
// (1, theta, phi) and (1, theta, phi)
// cosine( arc length ) =
// sin phi sin phi' cos(theta-theta') + cos phi cos phi'
// distance = rho * arc length
double cos = (Math.Sin(mePhi) * Math.Sin(itemPhi) * Math.Cos(meTheta - itemTheta) +
Math.Cos(mePhi) * Math.Cos(itemPhi));
double arc = Math.Acos(cos);
// Remember to multiply arc by the radius of the earth
// in your favorite set of units to get length.
return arc;
}
public static double CalculateBearing(Coords pointA, Coords pointB)
{
double lat1 = pointA.Latitude.ToRadian();
double lat2 = pointB.Latitude.ToRadian();
double deltaLong = (pointB.Longitude - pointA.Longitude).ToRadian();
double y = Math.Sin(deltaLong) * Math.Cos(lat2);
double x = Math.Cos(lat1) * Math.Sin(lat2) - (Math.Sin(lat1) * Math.Cos(lat2) * Math.Cos(deltaLong));
double initialBearing = Math.Atan2(y, x).ToDegrees();
double compassBearing = (initialBearing + 360) % 360;
return compassBearing;
}
public void FindNearest(Coords me, out Coords nearestItem, out double nearestDistance)
{
nearestItem = new Coords();
nearestDistance = double.NaN;
foreach (Coords item in this.Coordinates)
{
double itemDistance = SphericalDistance(me, item) * 3963.1676; // earth radius in miles
if (double.IsNaN(nearestDistance) || itemDistance < nearestDistance)
{
nearestItem = item;
nearestDistance = itemDistance;
}
}
}
public void SphericalDistance_Should_Return_10()
{
TestCoordinateResource resource = new TestCoordinateResource();
Coords here = new Coords
{
Latitude = 39.928780,
Longitude = -105.139314
};
Coords there = new Coords
{
Latitude = 39.927733,
Longitude = -105.147360
};
// these two coords are ~ less than 1/2 mile apart
var distance = resource.SphericalDistance(here, there) * 3963.1676; // earth radius in miles
Assert.That(distance <= 0.5);
}
