//
// Instance Methods
//
public double DistanceFrom(Location remoteLocation)
{
Verify(this);
Verify(remoteLocation);
return Haversine.CalculateDistance(this, remoteLocation);
}
/// <summary>
/// Creates a box that encloses the specified location, where the sides of the square
/// are inRadius miles away from the location at the perpendicular. Note that we do
/// not actually generate lat/lon pairs; we only generate the coordinate that
/// represents the side of the box.
/// </summary>
/// <remarks>
/// <para>Formula obtained from Dr. Math at http://www.mathforum.org/library/drmath/view/51816.html.</para>
/// </remarks>
/// <param name="inLocation"></param>
/// <param name="inRadius"></param>
/// <returns></returns>
public static RadiusBox Create(Location inLocation, double inRadius)
{
/*
A point {lat,lon} is a distance d out on the tc radial from point 1 if:
lat = asin (sin (lat1) * cos (d) + cos (lat1) * sin (d) * cos (tc))
dlon = atan2 (sin (tc) * sin (d) * cos (lat1), cos (d) - sin (lat1) * sin (lat))
lon = mod (lon1 + dlon + pi, 2 * pi) - pi
Where:
* d is the distance in radians (an arc), so the desired radius divided by
the radius of the Earth.
* tc = 0 is N, tc = pi is S, tc = pi/2 is E, tc = 3*pi/2 is W.
*/
double lat;
double dlon;
double dLatInRads = inLocation.Latitude * (Math.PI / 180.0);
double dLongInRads = inLocation.Longitude * (Math.PI / 180.0);
double dDistInRad = inRadius / Globals.EarthRadiusMiles;
RadiusBox box = new RadiusBox();
box.Radius = inRadius;
// N (tc == 0):
// lat = asin (sin(lat1)*cos(d) + cos(lat1)*sin(d))
// = asin (sin(lat1 + d))
// = lat1 + d
// Unused:
// lon = lon1, because north-south lines follow lines of longitude.
box.TopLine = dLatInRads + dDistInRad;
box.TopLine *= (180.0 / Math.PI);
// S (tc == pi):
// lat = asin (sin(lat1)*cos(d) - cos(lat1)*sin(d))
// = asin (sin(lat1 - d))
// = lat1 - d
// Unused:
// lon = lon1, because north-south lines follow lines of longitude.
box.BottomLine = dLatInRads - dDistInRad;
box.BottomLine *= (180.0 / Math.PI);
// E (tc == pi/2):
// lat = asin (sin(lat1)*cos(d))
// dlon = atan2 (sin(tc)*sin(d)*cos(lat1), cos(d) - sin(lat1)*sin(lat))
// lon = mod (lon1 + dlon + pi, 2*pi) - pi
lat = Math.Asin(Math.Sin(dLatInRads) * Math.Cos(dDistInRad));
dlon = Math.Atan2(Math.Sin(Math.PI / 2.0) * Math.Sin(dDistInRad) * Math.Cos(dLatInRads), Math.Cos(dDistInRad) - Math.Sin(dLatInRads) * Math.Sin(lat));
box.RightLine = ((dLongInRads + dlon + Math.PI) % (2.0 * Math.PI)) - Math.PI;
box.RightLine *= (180.0 / Math.PI);
// W (tc == 3*pi/2):
// lat = asin (sin(lat1)*cos(d))
// dlon = atan2 (sin(tc)*sin(d)*cos(lat1), cos(d) - sin(lat1)*sin(lat))
// lon = mod (lon1 + dlon + pi, 2*pi) - pi
dlon = Math.Atan2(Math.Sin(3.0 * Math.PI / 2.0) * Math.Sin(dDistInRad) * Math.Cos(dLatInRads), Math.Cos(dDistInRad) - Math.Sin(dLatInRads) * Math.Sin(lat));
box.LeftLine = ((dLongInRads + dlon + Math.PI) % (2.0 * Math.PI)) - Math.PI;
box.LeftLine *= (180.0 / Math.PI);
return box;
}
/// <summary>
/// Calculates the great-circle distance between two points on a sphere from their
/// longitudes and latitudes.
/// </summary>
/// <remarks>See: http://en.wikipedia.org/wiki/Haversine_formula</remarks>
/// <param name="loc1"></param>
/// <param name="loc2"></param>
/// <returns></returns>
public static double CalculateDistance(Location loc1, Location loc2)
{
/*
The Haversine formula according to Dr. Math.
http://mathforum.org/library/drmath/view/51879.html
dlon = lon2 - lon1
dlat = lat2 - lat1
a = (sin(dlat/2))^2 + cos(lat1) * cos(lat2) * (sin(dlon/2))^2
c = 2 * atan2(sqrt(a), sqrt(1-a))
d = R * c
Where
* dlon is the change in longitude
* dlat is the change in latitude
* c is the great circle distance in Radians.
* R is the radius of a spherical Earth.
* The locations of the two points in spherical coordinates (longitude and
latitude) are lon1,lat1 and lon2, lat2.
*/
double dDistance = double.MinValue;
double dLat1InRad = loc1.Latitude * (Math.PI / 180.0);
double dLong1InRad = loc1.Longitude * (Math.PI / 180.0);
double dLat2InRad = loc2.Latitude * (Math.PI / 180.0);
double dLong2InRad = loc2.Longitude * (Math.PI / 180.0);
double dLongitude = dLong2InRad - dLong1InRad;
double dLatitude = dLat2InRad - dLat1InRad;
// Intermediate result a.
double a = Math.Pow(Math.Sin(dLatitude / 2.0), 2.0) + Math.Cos(dLat1InRad) * Math.Cos(dLat2InRad) * Math.Pow(Math.Sin(dLongitude / 2.0), 2.0);
// Intermediate result c (great circle distance in Radians).
double c = 2.0 * Math.Atan2(Math.Sqrt(a), Math.Sqrt(1.0 - a));
// Distance.
dDistance = Globals.EarthRadiusMiles * c;
return dDistance;
}
static void DisplayLocation(Location location)
{
Console.WriteLine(location);
Console.WriteLine();
}
internal static void Verify(Location location)
{
if (location == null)
{
throw new ArgumentNullException("location");
}
if (location.Latitude == double.MinValue)
{
throw new ArgumentException("inLoc1.Latitude", string.Format("The database does not contain latitude information for {0}, {1}.", location.City, location.State));
}
if (location.Longitude == double.MinValue)
{
throw new ArgumentException("inLoc1.Longitude", string.Format("The database does not contain longitude information for {0}, {1}.", location.City, location.State));
}
}
