GPS Receivers, Geodesy, and Geocaching: Vincenty’s Formula

/* Gavaghan.Geodesy by Mike Gavaghan
 * 
 * http://www.gavaghan.org/blog/free-source-code/geodesy-library-vincentys-formula/
 * 
 * This code may be freely used and modified on any personal or professional
 * project.  It comes with no warranty.
 */
using System;
using System.Text;

namespace Gavaghan.Geodesy
{
  /// <summary>
  /// Encapsulation of latitude and longitude coordinates on a globe.  Negative
  /// latitude is southern hemisphere.  Negative longitude is western hemisphere.
  /// 
  /// Any angle may be specified for longtiude and latitude, but all angles will
  /// be canonicalized such that:
  /// 
  ///      -90 <= latitude <= +90
  ///     -180 < longitude <= +180
  /// </summary>
  [Serializable]
  public struct GlobalCoordinates : IComparable<GlobalCoordinates>
  {
    /// <summary>Latitude.  Negative latitude is southern hemisphere.</summary>
    private Angle mLatitude;

    /// <summary>Longitude.  Negative longitude is western hemisphere.</summary>
    private Angle mLongitude;

    /// <summary>
    /// Canonicalize the current latitude and longitude values such that:
    /// 
    ///      -90 <= latitude <= +90
    ///     -180 < longitude <= +180
    /// </summary>
    private void Canonicalize()
    {
      double latitude = mLatitude.Degrees;
      double longitude = mLongitude.Degrees;

      latitude = (latitude + 180) % 360;
      if (latitude < 0) latitude += 360;
      latitude -= 180;

      if (latitude > 90)
      {
        latitude = 180 - latitude;
        longitude += 180;
      }
      else if (latitude < -90)
      {
        latitude = -180 - latitude;
        longitude += 180;
      }

      longitude = ((longitude + 180) % 360);
      if (longitude <= 0) longitude += 360;
      longitude -= 180;

      mLatitude = new Angle(latitude);
      mLongitude = new Angle(longitude);
    }

    /// <summary>
    /// Construct a new GlobalCoordinates.  Angles will be canonicalized.
    /// </summary>
    /// <param name="latitude">latitude</param>
    /// <param name="longitude">longitude</param>
    public GlobalCoordinates(Angle latitude, Angle longitude)
    {
      mLatitude = latitude;
      mLongitude = longitude;
      Canonicalize();
    }

    /// <summary>
    /// Get/set latitude.  The latitude value will be canonicalized (which might
    /// result in a change to the longitude). Negative latitude is southern hemisphere.
    /// </summary>
    public Angle Latitude
    {
      get { return mLatitude; }
      set 
      { 
        mLatitude = value; 
        Canonicalize(); 
      }
    }

    /// <summary>
    /// Get/set longitude.  The longitude value will be canonicalized. Negative
    /// longitude is western hemisphere.
    /// </summary>
    public Angle Longitude
    {
      get { return mLongitude; }
      set 
      { 
        mLongitude = value; 
        Canonicalize(); 
      }
    }

    /// <summary>
    /// Compare these coordinates to another set of coordiates.  Western
    /// longitudes are less than eastern logitudes.  If longitudes are equal,
    /// then southern latitudes are less than northern latitudes.
    /// </summary>
    /// <param name="other">instance to compare to</param>
    /// <returns>-1, 0, or +1 as per IComparable contract</returns>
    public int CompareTo(GlobalCoordinates other)
    {
      int retval;

      if (mLongitude < other.mLongitude) retval = -1;
      else if (mLongitude > other.mLongitude) retval = +1;
      else if (mLatitude < other.mLatitude) retval = -1;
      else if (mLatitude > other.mLatitude) retval = +1;
      else retval = 0;

      return retval;
    }

    /// <summary>
    /// Get a hash code for these coordinates.
    /// </summary>
    /// <returns></returns>
    public override int GetHashCode()
    {
      return ((int)(mLongitude.GetHashCode() * (mLatitude.GetHashCode() + 1021))) * 1000033;
    }

    /// <summary>
    /// Compare these coordinates to another object for equality.
    /// </summary>
    /// <param name="obj"></param>
    /// <returns></returns>
    public override bool Equals(object obj)
    {
      if (!(obj is GlobalCoordinates)) return false;

      GlobalCoordinates other = (GlobalCoordinates)obj;

      return (mLongitude == other.mLongitude) && (mLatitude == other.mLatitude);
    }

    /// <summary>
    /// Get coordinates as a string.
    /// </summary>
    /// <returns></returns>
    public override string ToString()
    {
      StringBuilder builder = new StringBuilder();

      builder.Append(mLatitude.Abs().ToString());
      builder.Append((mLatitude >= Angle.Zero) ? 'N' : 'S');
      builder.Append(';');
      builder.Append(mLongitude.Abs().ToString());
      builder.Append((mLongitude >= Angle.Zero) ? 'E' : 'W');
      builder.Append(';');

      return builder.ToString();
    }
  }
}