/// <summary>
/// Distance from point to a line segment
/// </summary>
public static double SegmentPointDistance(WWVectorD2 edgeP1, WWVectorD2 edgeP2, WWVectorD2 point, double margin)
{
System.Diagnostics.Debug.Assert(margin < WWVectorD2.Distance(edgeP1, edgeP2));
// 直線の方程式 ax + by + c = 0
double dx = edgeP2.X - edgeP1.X;
double dy = edgeP2.Y - edgeP1.Y;
double a = dy;
double b = -dx;
double c = edgeP2.X * edgeP1.Y - edgeP2.Y * edgeP1.X;
// pointと最短距離の直線上の点の座標。
var nearestPointOnLine = new WWVectorD2(
(b * (+b * point.X - a * point.Y) - a * c) / (a * a + b * b),
(a * (-b * point.X + a * point.Y) - b * c) / (a * a + b * b));
if ((margin + nearestPointOnLine.X < edgeP1.X && margin + nearestPointOnLine.X < edgeP2.X) || //< 最短地点のx座標がedgeP1,edgeP2よりも左。
(margin + nearestPointOnLine.Y < edgeP1.Y && margin + nearestPointOnLine.Y < edgeP2.Y) || //< 最短地点のy座標がedgeP1,edgeP2よりも下。
(margin + edgeP1.X < nearestPointOnLine.X && margin + edgeP2.X < nearestPointOnLine.X) || //< 最短地点のx座標がedgeP1,edgeP2よりも右。
(margin + edgeP1.Y < nearestPointOnLine.Y && margin + edgeP2.Y < nearestPointOnLine.Y) //< 最短地点のy座標がedgeP1,edgeP2よりも上。
)
{
// 点と最短距離の直線上の点が線分の範囲外。
// edgeP1とedgeP2のうち、近い方が最短距離の線分上の点。
double d1 = WWVectorD2.Distance(edgeP1, point);
double d2 = WWVectorD2.Distance(edgeP2, point);
return((d1 < d2) ? d1 : d2);
}
// 直線と点の距離distance。
double distance = Math.Abs(a * point.X + b * point.Y + c) / Math.Sqrt(a * a + b * b);
return(distance);
}
/// <returns>a - b</returns>
static public WWVectorD2 Sub(WWVectorD2 a, WWVectorD2 b)
{
return(new WWVectorD2(a.X - b.X, a.Y - b.Y));
}
static public WWVectorD2 Add(WWVectorD2 a, WWVectorD2 b)
{
return(new WWVectorD2(a.X + b.X, a.Y + b.Y));
}
static public double Distance(WWVectorD2 a, WWVectorD2 b)
{
double d = Math.Sqrt((a.X - b.X) * (a.X - b.X) + (a.Y - b.Y) * (a.Y - b.Y));
return(d);
}