First observe Golden Dragon stirring not stirring, next examine blood vein identify incoming dragon.
The XuanKong Flying Star 玄空飛星, will interpret these 2 liners as the way Flying Star 飛星, supposed to fly. Note that the meaning of Golden Dragon represents Qian sector. In the Later Heaven BaGua, Qian is assigned to the northwest and receive the element of Metal and in Chinese means 金. Qian is also related to Dragon 龙 based on the notion of Yao change. Together one must observe if the Golden Dragon 金 龙 moves or not. If the star take flight it must start from the Qian palace. In the event of a missing sector in Qian, the entire Flying Star 飛星 chart cannot work! It also means if there is a vertical missing sector in Qian, Flying Star 飛星 chart also cannot work. The reason being the LoShu 洛书 flight takes 3 dimensional along the 3 dimensional of the Later Heaven BaGua.
HeTu in 3D: -
The early Chinese does not concern so much as to the sitting and facing of their homes. Their main concerns are the community. So, the EH is use to assist them in locating prosperous spots. It is all location, location and location.
EH BaGua is imagery, Xiang of the cosmos. To understand its attributes, EH Numerology is invented. This is another component called Li (method). So HeTu is derived to interpret the EH BaGua. HeTu is derived from the understanding of Qi, the 5 elements. As the saying goes, Heaven bestow, Earth receives, Qi originates from Heaven and settle underground as in the forms of mountain (Gen) and rivers (Dui). Such manifestation is called as above, so below. As above there are asterisms. As below there are mountains and rivers which we called Dragons. So, it is believed that the working mechanism of Qi must follow an order. This order is HeTu. So, Li, Qi and Xiang 里气象 are complete.
However, have we ever thought that HeTu is also in 3D?