Xuan Kong Da Gua (玄空大卦) reads a property rather than the people in it. It lays the 64 hexagrams of the I Ching around the compass, 5.625° each, and names the building by the two it straddles: the hexagram its facing bearing lies in, and the hexagram directly behind it. Those two are always a figure and its inverse, they share one period number (卦運), and that number is read against the 20-year period the calendar is in. No birth data enters any of it.
What a Xuan Kong Da Gua reading produces
Five things, all from one bearing. The facing hexagram — the ring segment the front of the building looks into. The sitting hexagram — the segment 180° away, behind the building. Their 卦運, a number from 1 to 9 (never 5) that the two always share. Their two 卦氣 numbers, the Early Heaven numbers of each upper trigram, which always sum to ten. And a verdict: whether the pair is timely in the current period, which holds when the 卦運 falls in the same half of the 180-year cycle (上元, 1–4; 下元, 6–9) as the period does. Period 9 runs from the Li Chun of 2024 to that of 2044 and belongs to 下元.
From compass bearing to hexagram pair
Take the facing bearing (see the calculation guide for how). Divide it by 5.625: the whole part, counted from due north, is the facing hexagram’s place on the ring. The ring runs in the Fu Xi order — 復 opens at due north and the hexagrams whose bottom line is solid run clockwise through the east to 乾, which closes at due south; 姤 opens at due south and the rest run on through the west to 坤, closing at due north. The sitting hexagram is the segment 32 places on. Because the ring is built this way, the segment opposite any hexagram is its 錯卦 — every one of the six lines flipped — which is why the two always share a 卦運 and why their 卦氣 always sum to ten.
Boundaries, and what the reading does not do
A segment is only 5.625° wide, and one line (爻) of it is 0.9375°. A facing within one line of a boundary is flagged, because a small measuring error would change the pair; a facing exactly on a boundary straddles two pairs, and if their 卦運 fall in different halves of the cycle the verdict waits on a finer bearing. The San Yuan schools also name two compass lines: a facing between two trigram palaces is 大空亡, one between two mountains of a palace 小空亡. What the reading does not do: it does not give each room or sector its own hexagram, and it does not grade the building against its occupants. KAXANTA computes the ring reading from the house facing saved in Settings.
References
Canonical sources that inform this guide.
- Feng Shui/Xuan Kong Da Gua/Compass Location · WEBSITE
- Feng Shui/Xuan Kong Da Gua/Binary Representation of the 64 Hexagrams · WEBSITE
- Bagua (Eight Trigrams) · WIKIPEDIA
- I Ching · WIKIPEDIA