public double VerticalHeight(clsPoint pt1)
{
//Returns the height of the line where is passes over p1
clsLine l1 = default(clsLine);
clsLine l2 = default(clsLine);
double d = 0;
double d1 = 0;
double d2 = 0;
l1 = new clsLine(P1.X, P1.Y, P2.X, P2.Y);
if (l1.IsOnLine(pt1) == false)
{
return(0);
}
d1 = l1.Length;
l1.Normalise();
l2 = new clsLine(l1.P1, pt1);
d2 = l1.Dot(l2);
d = d2 / d1;
return(P1.Z + (P2.Z - P1.Z) * d);
}
