/// <summary>
/// Gets the distance (in km) from Point A to Point B (both A and B must lie on a polyline defined by a list of points).
/// If B is before A, the distance is negative!
/// </summary>
/// <param name="A">First point</param>
/// <param name="B">Second point</param>
/// <param name="points">List of Points that define the polyline</param>
/// <returns></returns>
public static double GetDistanceOnPolyline(PointLatLng A, PointLatLng B, List<PointLatLng> points)
{
double dist = 0d;
//If both points are the same return 0!
if (A == B)
return dist;
bool foundA = false;
bool foundB = false;
double distP1toA, distP2toA, distP1toB, distP2toB, distP1toP2;
for (int i = 0; i < points.Count - 1; i++)
{
var p1 = points[i];
var p2 = points[i + 1];
bool AisBetween = GMapUtils.IsPointOnLineSegment(p1, p2, A, out distP1toA, out distP2toA, out distP1toP2);
if (AisBetween)
foundA = true;
bool BisBetween = GMapUtils.IsPointOnLineSegment(p1, p2, B, out distP1toB, out distP2toB, out distP1toP2);
if (BisBetween)
foundB = true;
if (AisBetween && BisBetween)
{
dist = GMapProviders.EmptyProvider.Projection.GetDistance(A, B);
if (distP1toB < distP1toA)
dist *= -1d;
return dist;
}
//Point A was found, but not B:
if (AisBetween && !foundB)
dist += distP2toA;
else if (foundA && !AisBetween && !foundB)
dist += distP1toP2;
else if (foundA && !AisBetween && BisBetween)
{
dist += distP1toB;
break;
}
//Point B was found, but not A:
else if (BisBetween && !foundA)
dist += distP2toB;
else if (foundB && !BisBetween && !foundA)
dist += distP1toP2;
else if (foundB && !BisBetween && AisBetween)
{
dist += distP1toA;
dist *= -1d;
break;
}
}
if (!foundA || !foundB)
throw new Exception("Point A or Point B (or both) are not on the polyline!");
return dist;
}
/// <summary>
/// Returns a point that lies on the polyline defined by the point list, and is a certain distance (in km!) from point A (that must also lie on the polyline).
/// If the point would lie outside of the polyline, the last point of the polyline is returned!
/// If the distance is negative, the new point lies BEFORE the given point!
/// </summary>
/// <param name="A">The Start point</param>
/// <param name="dist">The distance from the start point in km</param>
/// <param name="points">The points defining the polyline</param>
/// <returns></returns>
public static PointLatLng GetDistantPointOnPolyline(PointLatLng A, double distance, List<PointLatLng> points)
{
if (distance == 0d)
return A;
PointLatLng newPoint = new PointLatLng();
double distP1toA, distP2toA, distP1toP2;
double fooDist = 0d, lastDist = 0d, newDist = 0d;
if (distance > 0d)
{
for (int i = 0; i < points.Count - 1; i++)
{
var p1 = points[i];
var p2 = points[i + 1];
if (GMapUtils.IsPointOnLineSegment(p1, p2, A, out distP1toA, out distP2toA, out distP1toP2))
{
fooDist = distP2toA;
while (i < points.Count - 2 && fooDist < distance)
{
i++;
p1 = points[i];
p2 = points[i + 1];
lastDist = GMapProviders.EmptyProvider.Projection.GetDistance(p1, p2);
fooDist += lastDist;
}
if (fooDist < distance)
return points.Last();
double bearing = GMapProviders.EmptyProvider.Projection.GetBearing(p1, p2);
//Case 1: Last Distance is greater than 0 (the while loop ran at least one time)
if (lastDist > 0d)
{
newDist = lastDist - (fooDist - distance);
newPoint = GMapUtils.GetClosestPointOnPolyline(points, GMapUtils.GetPointLatLngFromStartPoint(p1, bearing, newDist));
}
//Case 2: Last Distance is 0, the while loop was not called:
else
{
newPoint = GMapUtils.GetClosestPointOnPolyline(points, GMapUtils.GetPointLatLngFromStartPoint(A, bearing, distance));
}
break;
}
}
}
else
{
for (int i = 0; i < points.Count - 1; i++)
{
var p1 = points[i];
var p2 = points[i + 1];
if (GMapUtils.IsPointOnLineSegment(p1, p2, A, out distP1toA, out distP2toA, out distP1toP2))
{
fooDist = distP1toA;
while (i > 0 && fooDist < Math.Abs(distance))
{
i--;
p1 = points[i];
p2 = points[i + 1];
lastDist = GMapProviders.EmptyProvider.Projection.GetDistance(p1, p2);
fooDist += lastDist;
}
if (fooDist < Math.Abs(distance))
return points.First();
double bearing = GMapProviders.EmptyProvider.Projection.GetBearing(p2, p1);
//Case 1: Last Distance is greater than 0 (the while loop ran at least one time)
if (lastDist > 0d)
{
newDist = lastDist - (fooDist - Math.Abs(distance));
newPoint = GMapUtils.GetClosestPointOnPolyline(points, GMapUtils.GetPointLatLngFromStartPoint(p2, bearing, newDist));
}
//Case 2: Last Distance is 0, the while loop was not called:
else
newPoint = GMapUtils.GetClosestPointOnPolyline(points, GMapUtils.GetPointLatLngFromStartPoint(A, bearing, Math.Abs(distance)));
break;
}
}
}
return newPoint;
}