/// <summary>
/// Calculate how far the point is along a track from the start-point, heading towards the end-point.
/// <para>That is, if a perpendicular is drawn from the point to the (great circle) path, the along-track distance is the distance from the start point to where the perpendicular crosses the path.</para>
/// </summary>
/// <param name="pointA">The point to calculate the distance from.</param>
/// <param name="startPoint">Start point of great circle path.</param>
/// <param name="endPoint">End point of great circle path.</param>
/// <param name="radius">Radius of earth.</param>
/// <returns>The distance along great circle to point nearest point A in the same units as the radius.</returns>
public double AlongTrackDistance(ICoordinate pointA, ICoordinate startPoint, ICoordinate endPoint, double radius)
{
if (pointA == null)
{
throw new ArgumentNullException(nameof(pointA), "The argument cannot be null.");
}
if (startPoint == null)
{
throw new ArgumentNullException(nameof(startPoint), "The argument cannot be null.");
}
if (endPoint == null)
{
throw new ArgumentNullException(nameof(endPoint), "The argument cannot be null.");
}
ValidateRadius(radius);
var δ13 = startPoint.DistanceTo(pointA, radius) / radius;
var θ13 = startPoint.BearingTo(pointA).ToRadians();
var θ12 = startPoint.BearingTo(endPoint).ToRadians();
var δxt = Math.Asin(Math.Sin(δ13) * Math.Sin(θ13 - θ12));
var δat = Math.Acos(Math.Cos(δ13) / Math.Abs(Math.Cos(δxt)));
var result = δat * Math.Sign(Math.Cos(θ12 - θ13)) * radius;
return(result);
}
public ICoordinate FindNearest(ICoordinate aPoint)
{
var mc = aPoint.HilbertIndex();
var nearestGuess = orderedData.Values[orderedIndexes.FindNearestIndex(mc)][0];
var guessDist = aPoint.DistanceTo(nearestGuess);
var offsetPOI = new PointOfInterest(guessDist, guessDist);
var minmc = (aPoint.Minus(offsetPOI)).HilbertIndex();
var minmci = orderedIndexes.FindNearestIndex(minmc);
var maxmc = (aPoint.Plus(offsetPOI)).HilbertIndex();
var maxmci = orderedIndexes.FindNearestIndex(maxmc);
for (int j2 = minmci; j2 < maxmci; ++j2)
{
var tryList = orderedData.Values[j2];
for (int j3 = 0; j3 < tryList.Count; ++j3)
{
var y = tryList[j3];
var ydist = ((y.Longitude - aPoint.Longitude) * (y.Longitude - aPoint.Longitude) + (y.Latitude - aPoint.Latitude) * (y.Latitude - aPoint.Latitude));
if (ydist < guessDist)
{
nearestGuess = y;
guessDist = ydist;
}
}
}
return(nearestGuess);
}