.. module:: vespa.orbits
If they represent binary or triple star systems, :class:`vespa.stars.StarPopulation` objects are created with a large population of randomized orbits. This is done using the :class:`OrbitPopulation` and :class:`TripleOrbitPopulation` objects.
The engine that makes it possible to initialize large numbers of random orbital positions nearly instantaneously is the :func:`kepler.Efn` function (as used by :func:`utils.orbit_posvel`), which uses a precomputed grid to interpolate the solutions to Kepler's equation for a given mean anomaly and eccentricity (or arrays thereof).
The final coordinate system of these populations is
"observer-oriented," with the z axis along the line of sight, and
the x-y plane being the plane of the sky. Practically, this is
accomplished by first simulating all the random orbits in the x-y
plane, and then "observing" them from lines of sight randomly oriented
on the unit sphere, and projecting appropriately.
Coordinates are handled using :class:`astropy.coordinates.SkyCoord` objects.
.. autoclass:: vespa.orbits.populations.OrbitPopulation :members:
.. autoclass:: vespa.orbits.populations.TripleOrbitPopulation :members:
The following functions are used in the creation of :class:`OrbitPopulation` objects. :func:`kepler.Efn` is used for instanteous solution of Kepler's equation (via interpolation), and :func:`utils.orbit_posvel` does the projecting of random orbits into 3-d Cartesian coordinates, assisted by :func:`utils.orbitproject` and :func:`utils.random_spherepos`.
.. autofunction:: vespa.orbits.kepler.Efn
.. autofunction:: vespa.orbits.utils.orbit_posvel
.. autofunction:: vespa.orbits.utils.orbitproject
.. autofunction:: vespa.orbits.utils.random_spherepos