docs: note that calculate_planets applies ayanamsa via naive subtraction#9
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Adds a short subsection under "Advanced: Planetary Positions & Dignity" describing the observed ayanamsa-application behaviour of `calculate_planets(jd, mode)` and how to opt into the SEFLG_SIDEREAL flag path via `calc_ut` if needed. Observations are framed as external testing notes (not statements about internals). Goal is to help future users who cross-check positions against KP / Vedic stacks like VedicRishi avoid the ~6″ surprise.
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Summary
Adds a short subsection to the
calculate_planetsexample in the README documenting an observation from external testing: the returned sidereal longitudes matchswe_calc(jd, planet, TROPICAL) − swe_get_ayanamsa(jd)rather than Swiss-Ephemeris'sSEFLG_SIDEREALflag path. The two agree to first order but differ by ~3–6″ per planet.This is the convention most KP / legacy Vedic software uses, so for many readers it's the desired behaviour — the note is just so future users don't have to rediscover this when comparing against other stacks.
The note also shows how to opt into the
SEFLG_SIDEREALpath viacalc_ut, leveraging the side-effect thatcalculate_planetssets the global sidereal mode (so a subsequentcalc_ut(..., SEFLG_SIDEREAL)returns positions in the expected ayanamsa frame).Scope
Related
Wraps up the investigation in #8.
Test plan