---
title: "Primary Directions (主限向運法)"
method: GET
path: "/api/trpc/progressions.primaryDirections"
tags: ["Western"]
---

# Primary Directions (主限向運法)

`GET /api/trpc/progressions.primaryDirections`

## Request

- Base URL: `https://api.asktian.com`
- URL: `https://api.asktian.com/api/trpc/progressions.primaryDirections`
- Auth: HTTP bearer

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`.

## Query parameters

- `input` string

## Response `200`

tRPC result envelope

- TrpcResult: tRPC HTTP response envelope.
  - `result` object
    - `data` object: The procedure's return value (system-specific).

---

[API](https://skmtc.dev/asktian/apis/asktian-metaphysics-api.md) · [All operations](https://skmtc.dev/asktian/apis/asktian-metaphysics-api/llms.txt) · [OpenAPI document](https://skmtc.dev/asktian/apis/asktian-metaphysics-api/revisions/3c8fdc979206?raw)