/// <summary>
/// Computes the distance from a point p to a line segment AB.
/// Note: NON-ROBUST!
/// </summary>
/// <param name="p">The point to compute the distance for.</param>
/// <param name="a">One point of the line.</param>
/// <param name="b">Another point of the line (must be different to A).</param>
/// <returns> The distance from p to line segment AB.</returns>
public static double DistancePointLine(MPoint p, MPoint a, MPoint b)
{
// if start == end, then use pt distance
if (a.Equals(b))
{
return(p.Distance(a));
}
// otherwise use comp.graphics.algorithms Frequently Asked Questions method
/*(1) AC dot AB
* r = ---------
||AB||^2
*
* r has the following meaning:
* r=0 Point = A
* r=1 Point = B
* r<0 Point is on the backward extension of AB
* r>1 Point is on the forward extension of AB
* 0<r<1 Point is interior to AB
*/
var r = ((p.X - a.X) * (b.X - a.X) + (p.Y - a.Y) * (b.Y - a.Y))
/
((b.X - a.X) * (b.X - a.X) + (b.Y - a.Y) * (b.Y - a.Y));
if (r <= 0.0)
{
return(p.Distance(a));
}
if (r >= 1.0)
{
return(p.Distance(b));
}
/*(2)
* (Ay-Cy)(Bx-Ax)-(Ax-Cx)(By-Ay)
* s = -----------------------------
* Curve^2
*
* Then the distance from C to Point = |s|*Curve.
*/
var s = ((a.Y - p.Y) * (b.X - a.X) - (a.X - p.X) * (b.Y - a.Y))
/
((b.X - a.X) * (b.X - a.X) + (b.Y - a.Y) * (b.Y - a.Y));
return(Math.Abs(s) * Math.Sqrt((b.X - a.X) * (b.X - a.X) + (b.Y - a.Y) * (b.Y - a.Y)));
}
