swiss-house-system-overlays-1.0.0 requests Equal E, Porphyry O, Alcabitius B, Regiomontanus R, and Placidus P through Swiss Ephemeris at the chart Julian day and terrestrial coordinates. Each successful result preserves twelve normalized cusps and a house number for every traditional planet.
Planet-position contract
The engine obtains ARMC from the house calculation and true obliquity from Swiss Ephemeris. It then calls swe_house_pos with ARMC, latitude, true obliquity, and each planet longitude and latitude. This avoids assigning planets with a hand-written cusp string or sign heuristic.
Unavailable-system contract
Swiss Ephemeris documents that some systems cannot be computed at polar latitudes. If the requested call fails, Stelliums records that named system as unavailable with null cusps and null planet assignments. It does not accept a library fallback or relabel another system as the requested output.
Regression evidence
- Dallas requires five available twelve-cusp outputs and seven planet-house assignments per system.
- The Dallas Sun remains at 295.354022 degrees while its Equal house is 9 and its Porphyry, Alcabitius, Regiomontanus, and Placidus houses are 10.
- The Tromsø fixture requires four available systems and one explicit unavailable Placidus record with no cusp or planet-house substitute.
- Rendered-chart verification requires five selectable overlays, twelve visible lines for the active system, a persistent device preference, and an inspectable technical ledger.
Interpretive boundary
The official technical source establishes algorithms and failure behavior, not a universal historical preference or a complete interpretive corpus for every system. Stelliums therefore exposes the geometry while retaining Whole Sign for governed topical techniques.