PointF p = new PointF(116.305671f, 39.966051f);

PointF p2 = new PointF(116.595428f, 39.828327f);

double value = Math.Sqrt(Math.Abs(p.X - p2.X) * Math.Abs(p.X - p2.X) + Math.Abs(p.Y - p2.Y) * Math.Abs(p.Y - p2.Y));