Detailed process of experts set up rendezvous and docking points because four parking

Shenzhou VIII spacecraft with Temple One goal of the first aircraft to enter the self-guided rendezvous and docking segment, from 5 km to the close distance of 30 meters between the front and rear parking were set up four points in each point to be parked for short stay. So, why set up four parking point? ...Detailed process of experts set up rendezvous and docking points because four parking