  Aims. We aim to determine the geometry, density gradient, and velocity
structure of jets in post-asymptotic giant branch (post-AGB) binaries. Methods.
Our high cadence time series of high-resolution optical spectra of jet-creating
post-AGB binary systems provide us with a unique tomography of the jet. We
determine the spatio-kinematic structure of the jets based on these data by
fitting the synthetic spectral line profiles created by our model to the
observed, orbital phase-resolved, H{\alpha}-line profiles of these systems. The
fitting routine is provided with an initial spectrum and is allowed to test
three configurations, derived from three specific jet launching models: a
stellar jet launched by the star, an X-wind, and a disk wind configuration. We
apply a Markov-chain Monte Carlo routine in order to fit our model to the
observations. Our fitting code is tested on the post-AGB binary IRAS19135+3937.
Results. We find that a model using the stellar jet configuration gives a
marginally better fit to our observations. The jet has a wide half-opening
angle of about 76 degrees and reaches velocities up to 870 km/s. Conclusions.
Our methodology is successful in determining some parameters for jets in
post-AGB binaries. The model for IRAS19135+3937 includes a transparent, low
density inner region (for a half-opening angle < 40 degrees). The source
feeding the accretion disk around the companion is most likely the circumbinary
disk. We will apply this jet fitting routine to other jet-creating post-AGB
stars in order to provide a more complete description of these objects.
