In geomantic omen, the cave field is the center, which has five necessary conditions: cave, famous hall, sand prevention, mountain case and mountain proximity. The sand barrier on the left is also called Qinglong sand, and the sand barrier on the right is also called Baihusha, both of which play the role of barrier protection. If there is an extension of Qinglong's sand protection, turn right to make a mountain case in front of the cave, it is called "Qinglong commits a crime"; White tiger sand extends in front of the cave and turns left to come back to work, which is called "White tiger committing crimes". White tiger sand must be lower or the same as Qinglong sand.