In recent years, metasurfaces have emerged as promising components for reducing the size and complexity of optical imaging systems. Nevertheless, their incorporation into these systems remains a challenge due to the difference between the numerical tools used in the design of conventional imaging systems (ray tracing) and the design of metasurfaces (full-wave solvers). In this paper, we describe a methodology that combines the local periodicity approximation and a free space propagation technique to rapidly compute the optical response of a large-scale metasurface. We then explain the coupling of this fast solver with a ray tracer to accurately simulate an optical system containing a metasurface.