Primary Directions (主限向運法)

Western astrology's OLDEST predictive technique (Ptolemy, Tetrabiblos III → Placidus → Gansten): after birth the heavens keep turning ~1° every 4 minutes, and a direction is the arc of that primary motion carrying a promissor (a planet or its aspect point) to the natal mundane place of a significator (the four angles, or the Sun/Moon in mundo). Placidus semi-arc method, in zodiaco without latitude (the classical convention), ported from the open-source Morinus reference implementation: directions to the angles by pure ascension differences (MC by right ascension, ASC by oblique ascension), to the luminaries by the semi-arc proportion; direct and converse arcs served separately; Naibod (0°59′08″ = 1 year) and Ptolemy (1° = 1 year) keys. VERIFIED against the published Gadbury/Henry II worked example to the arcminute (Mars to the Ascendant: arc 40°18′, Naibod ~40y — the direction Gauricus' famous warning rode on), with every served arc re-proven by a rotation oracle. Symbolic timing, not a predictor of events.

Cost: 2 TIAN Points per call. tRPC procedure progressions.primaryDirections.