Positive? The rail is bent into an arc on a curved track. The radius of the rail is stretched at the front and rear ends with a 20-meter-long rope, and the vector from the middle of the rope to the rail is measured, which is called the positive vector. The magnitude of the positive vector is inversely proportional to the orbital radius.

In the daily maintenance of public works, the rope alignment method is used to adjust the curve direction, and the planned normal vector may be revised twice in the distribution calculation. The purpose of the first revision is to ensure that the distribution at the end of the curve is zero; The purpose of the second modification is to reduce or zero the dialing volume of some control points as much as possible.