For example, people: students in a class generally give students a positive attitude. Then when judging, let yourself judge the direction you are facing. There is also the problem of queuing, the same as above. For example, objects: generally, they are mainly on the left and right sides of the plane.

Brief introduction of reference object:

The whole extended space is fixedly connected with the reference body. The reference object is another object, which is selected as the standard to determine the position of the object and describe its mechanical motion. In order to represent the position of an object by numbers, a coordinate system can be set on the reference object, which is called the reference coordinate system. Both the reference frame and the reference coordinate system can be selected arbitrarily, but the same motion has different forms in different reference frames.

Usually, the appropriate reference body is selected according to the actual situation of the problem. For example, when a rocket takes off from the earth's surface, it should take the earth as a reference; When the spacecraft becomes an artificial planet orbiting the sun, it is desirable to take the sun as a reference. It can be seen that all mechanical phenomena can only be observed, described and studied relative to the selected reference system.

There may be different reference coordinate systems in the same reference system, which have different values for the position coordinates of the same object, but they are linked by certain geometric relations. In order to quantitatively describe the motion of an object, the reference coordinate system is often quoted directly.