swisseph 0.1.0

Isolate-safe Dart FFI bindings to the Swiss Ephemeris C library.

swisseph

Dart FFI bindings to the Swiss Ephemeris C library.

Compute planetary positions, house cusps, ayanamsa values, and rise/set times — with no code generation, no Flutter dependency, and full isolate safety.

Features

• 15 methods covering positions, houses, ayanamsa, rise/set, date conversion, and configuration
• All 47 standard ayanamsas — Lahiri, Fagan-Bradley, Raman, Krishnamurti, and 43 more
• 11 house systems — Placidus, Koch, Whole Sign, Campanus, Equal, and more
• Three ephemeris engines — Moshier (no files needed), Swiss Ephemeris (.se1 files), JPL
• Multiple coordinate systems — tropical, sidereal, heliocentric, barycentric, equatorial
• Isolate-safe — each instance wraps its own DynamicLibrary; copy the .so per isolate for independent C global state
• Instance-based API — no singletons, no hidden state
• Native asset build hook — dart pub get compiles the vendored C source automatically via CBuilder

Platform support

Platform	Status
Linux	Supported (gcc/clang)
macOS	Supported (clang)
Windows	Supported (MSVC)

Requires Dart SDK 3.11+ and a C compiler.

Install

dart pub add swisseph

Or add it to your pubspec.yaml directly:

dependencies:
  swisseph: ^0.1.0

Alternatively, install from the Git repository:

dependencies:
  swisseph:
    git:
      url: https://gitlab.com/ninthhouse/swisseph.dart
      ref: master

Then run dart pub get, which triggers the native build hook to compile the C source.

Quick start

import 'package:swisseph/swisseph.dart';

void main() {
  final swe = SwissEph.find();

  // Julian Day for 2000-01-01 12:00 UT
  final jd = swe.julday(2000, 1, 1, 12.0);

  // Sun position (Moshier — no data files needed)
  final sun = swe.calcUt(jd, seSun, seflgMoseph | seflgSpeed);
  print('Sun: ${sun.longitude}°');

  // Sidereal position (Lahiri)
  swe.setSidMode(seSidmLahiri);
  final sidSun = swe.calcUt(
    jd, seSun, seflgMoseph | seflgSpeed | seflgSidereal,
  );
  print('Sidereal Sun: ${sidSun.longitude}°');

  // House cusps (Campanus, Washington DC)
  final houses = swe.houses(jd, 38.8977, -77.0365, hsysCampanus);
  print('Ascendant: ${houses.ascendant}°');
  print('MC: ${houses.mc}°');

  // Sunrise
  final rise = swe.riseTrans(
    jd, seSun,
    rsmi: seCalcRise, geolon: -77.0365, geolat: 38.8977,
  );
  print('Sunrise JD: ${rise.transitTime}');

  swe.close();
}

See example/example.dart for a fuller example with formatted output.

API reference

Category	Methods
Date/time	julday, revjul
Config	setEphePath, setSidMode, setTopo, close, version
Positions	calcUt
Houses	houses
Ayanamsa	getAyanamsaUt, getAyanamsaExUt, getAyanamsaName
Names	getPlanetName, houseName
Rise/set	riseTrans
Utilities	degnorm

All native memory uses calloc + try/finally free. Errors throw SweException.

Ephemeris modes

Mode	Flag	Files needed	Accuracy
Moshier	seflgMoseph	None	~1 arcsecond
Swiss Ephemeris	seflgSwieph	.se1 data files	Sub-arcsecond
JPL	seflgJpleph	JPL ephemeris files	Highest

Moshier is a good default — it works out of the box with no data files.

For higher precision, download .se1 files from astro.com/ftp/swisseph/ephe into an ephe/ directory alongside your project, then point to them:

swe.setEphePath('ephe');
final sun = swe.calcUt(jd, seSun, seflgSwieph | seflgSpeed);

The ephemeris data files are not included in this package — you download them separately as needed. The three file sets are:

• sepl_*.se1 — main planets
• semo_*.se1 — Moon
• seas_*.se1 — asteroids (Chiron, Ceres, etc.)

Each file covers 600 years. Download the ranges you need.

Constants

Integer constants, not enums. Defined in lib/src/constants.dart.

Prefix	Purpose	Example
se	Body IDs	seSun, seMoon
seflg	Calculation flags	seflgSpeed
hsys	House systems	hsysPlacidus
seSidm	Ayanamsa modes	seSidmLahiri
seCalc	Rise/set flags	seCalcRise

Isolate safety

dlopen deduplicates shared libraries by device+inode. Two isolates loading the same .so path share C global state — sidereal mode, ephemeris path, and topocentric coordinates all leak between them.

The fix: copy the .so to a unique temp path per isolate. Each copy gets its own C globals.

// Copy the .so for this isolate
final tmpDir = Directory.systemTemp.createTempSync('swe_');
final libPath = '${tmpDir.path}/libswisseph_$id.so';
File(sharedLibPath).copySync(libPath);

final swe = SwissEph(libPath);

See test/isolate_test.dart for the full pattern. The stress test runs 3.06 billion calculations across 100 isolates to prove this holds at scale.

Limitations

• No Flutter plugin — this is a pure Dart package using native asset build hooks. Works with Dart CLI and can be used from Flutter, but is not a Flutter plugin.
• No asteroid files — only the bodies built into the Swiss Ephemeris core (Sun through Chiron, nodes, apogees) are exposed. Numbered asteroids via seAstOffset require additional .se1 files and are untested.
• C global state — the underlying C library uses global state. See Isolate safety above.

Tests

dart test

• 26 unit tests across date, calc, houses, ayanamsa, and isolate safety
• 545-value cross-validation suite against pyswisseph covering 13 bodies, 14 ayanamsas, 11 house systems, 7 locations, 7 dates
• Stress test: 3.06 billion calculations across 100 isolates (Moshier + Swiss Ephemeris, all 47 ayanamsas, heliocentric, barycentric, equatorial). See test/stress-test.md.

License

This Dart package is licensed under AGPL-3.0-or-later.

The Swiss Ephemeris C library (vendored in csrc/) is copyright Astrodienst AG and dual-licensed under AGPL-3.0 and a commercial license. See astro.com/swisseph for commercial licensing details.

Issues and contributions

File issues and merge requests on GitLab.