三维空间求最小距离应用场景的点滴疑问

public static Point MiniDistance(Point a, Point b, Point p, out float min_distance)
        {
            Vector i = b - a;
            double t = DotProduct(i, p - a) / DotProduct(i, i);
            if (t < 0.0)
            {
                min_distance = (float)(p - a).Length;
                return a;
            }
            if (t > 1.0)
            {
                min_distance = (float)(p - b).Length;
                return b;
            }
            Point result = a + t * i;
            min_distance = (float)(p - result).Length;
            return result;
        }

    private static double DotProduct(Vector m, Vector n)
        {
            return m.X * n.X + m.Y * n.Y;
        }