A computing code has been developed to simulate the center-to-limb variation (CLV) of the bisector's shape, and absolute wavelength shift of the core in strong photospheric lines. Observational results concerning these aspects are also reported for the K I 7699 line. In the numerical simulation, granulation is represented, as a first approximation, by means of the granular model by Nelson (1978). It appears that granulation alone does not reproduce the observations and thus some modification has to be implemented in the dynamical model employed. A good match to the observed CLV of the wavelength shift of the line core is achieved by adding two 8-min period gravity waves with horizontal wavelength of the granular scale, the only difference between them being the sign of their horizontal wavenumber. Changes in the phase difference between the oscillating parameters have a decisive influence on the result.