  Context. The correct modeling of the scattering polarization signals observed
in several strong resonance lines requires taking partial frequency
redistribution (PRD) phenomena into account. Aims. This work aims at assessing
the impact and the range of validity of the angle-averaged AA approximation
with respect to the general angle-dependent (AD) treatment of PRD effects in
the modeling of scattering polarization in strong resonance lines, with focus
on the solar Ca i 4227 {\AA} line. Methods. Spectral line polarization is
modeled by solving the radiative transfer problem for polarized radiation,
under nonlocal thermodynamic equilibrium conditions, taking PRD effects into
account, in static one-dimensional semi-empirical atmospheric models presenting
arbitrary magnetic fields. The problem is solved through a two-step approach.
In step 1, the problem is solved for intensity only, considering a multi-level
atom. In step 2, the problem is solved including polarization, considering a
two-level atom with an unpolarized and infinitely sharp lower level, and fixing
the lower level population calculated at step 1. Results. The results for the
Ca i 4227 {\AA} line show a good agreement between the AA and AD calculations
for the Q/I and U/I wings signals. However, AA calculations reveal an
artificial trough in the line-core peak of the linear polarization profiles,
whereas AD calculations show a sharper peak in agreement with observations.
Conclusions. An AD treatment of PRD effects is essential to correctly model the
line-core peak of the scattering polarization signal of the Ca i 4227 {\AA}
line. By contrast, in the considered static case, the AA approximation seems to
be suitable to model the wing scattering polarization lobes and their magnetic
sensitivity through magneto-optical effects.
