The psoap.orbit module is the backbone for the main PSOAP tasks of computing radial velocities to shift the wavelength vectors. For a description of the various radial velocity orbital models, see models. There is also an additional module included within the PSOAP packaged, psoap.orbit_astrometry, which is not used for the main Gaussian process routines, but includes functions for jointly modeling radial velocity measurements and relative astrometric measurements.
psoap.orbit
This is an alternate parameterization suited for joint astrometric and radial velocity orbital modeling.
psoap.orbit_astrometry