/// <summary>
/// Calculates the distance between two points on the ellipsoid given elevations.
///
/// First finded a new ellipsoid which radius is greater (or less) than the radius of the original ellipsoid
/// by the difference between the elevations. Then calculated the length of a geodesic on this ellipsoid. The
/// distance between two points is calculated as the hypotenuse of a triangle, which cathetus are geodesic
/// length and height difference.
/// </summary>
/// <param name="refEllipsoid">Ellipsoid</param>
/// <param name="start">A start point</param>
/// <param name="end">An end point</param>
/// <returns>An object that represents the result</returns>
public GeodeticMeasurement CalculateGeodeticMeasurement(Ellipsoid refEllipsoid, GlobalPosition start, GlobalPosition end)
{
GlobalCoordinates startCoords = start.Coordinates;
GlobalCoordinates endCoords = end.Coordinates;
// calculate the average elevation
double elev1 = start.Elevation;
double elev2 = end.Elevation;
double elev12 = (elev1 + elev2) / 2.0;
// compute the difference latitudes
double phi1 = startCoords.Latitude.Radians;
double phi2 = endCoords.Latitude.Radians;
double phi12 = (phi1 + phi2) / 2.0;
// Calculate new ellipsoid
double refA = refEllipsoid.SemiMajorAxis;
double f = refEllipsoid.IsInvFDefinitive ? 1 / refEllipsoid.InverseFlattening : 0;
double a = refA + elev12 * (1.0 + f * Math.Sin(phi12));
Ellipsoid ellipsoid = new Ellipsoid(a, f == 0 ? a : 0, f == 0 ? 0 : 1 / f, f != 0, LinearUnit.Metre, string.Empty, string.Empty, 0, string.Empty, string.Empty, string.Empty);
// calculate the geodesic on an average elevation
GeodeticCurve averageCurve = CalculateGeodeticCurve(ellipsoid, startCoords, endCoords);
return(new GeodeticMeasurement(averageCurve, elev2 - elev1));
}
/// <summary>
/// Initializes a new instance of the MapAround.Geography.GeodeticMeasurement.
/// </summary>
/// <param name="averageCurve">A segment of a geodesic line at the average elevation</param>
/// <param name="elevationChange">A change of the elevation in units of the ellipsoid's axes</param>
public GeodeticMeasurement(GeodeticCurve averageCurve, double elevationChange)
{
double ellDist = averageCurve.EllipsoidalDistance;
_curve = averageCurve;
_elevationChange = elevationChange;
_P2P = Math.Sqrt(ellDist * ellDist + _elevationChange * _elevationChange);
}
