  The mutual orbital alignment in multiple planetary systems is an important
parameter for understanding their formation. There are a number of elaborate
techniques to determine the alignment parameters using photometric or
spectroscopic data. Planet--planet occultations (PPOs), which can occur in
multiple transiting systems, are one intuitive example. While the presence of
PPOs constrains the orbital alignment, the absence at first glance does not.
Planetary systems, for which the measurement of orbital obliquities with
conventional techniques remains elusive, call for new methods whereby at least
some information on the alignments can be obtained. Here we develop a method
that uses photometric data to gain this kind of information from multi-transit
events. In our approach we synthesize multi-transit light curves of the
exoplanets in question via the construction of a grid of projected orbital tilt
angles $\alpha$, while keeping all transit parameters constant. These model
light curves contain PPOs for some values of $\alpha$. To compute the model
light curves, we use the 3D animation software Blender for our transit
simulations, which allows the use of arbitrary surface brightness distributions
of the star, such as limb darkening from model atmospheres. The resulting model
light curves are then compared to actual measurements. We present a detailed
study of the multi-transiting planetary system Kepler-20, including parameter
fits of the transiting planets and an analysis of the stellar activity. We
apply our method to Kepler-20 b and c, where we are able to exclude some
orbital geometries, and find a tendency of these planets to eclipse in front of
different stellar hemispheres in a prograde direction. [...]
