Influence of the precalculation module. Column density maps for three directions not aligned with the cartesian directions for the case of calculation in situ (top), using the precalculation module (middle), and the relative difference map (bottom). The azimuthal angle is fixed at φ = 0, and from left to right the polar angle is θ = 0.841,0.644,0.541 rad. The mean fractional difference, defined as in Eq. (12), are ΔN = 6.3,6.6,6.8%, respectively.