Upper left: sketch of the model being rotated; the homogeneous ISM inflow comes from the positive x-direction. Upper right: sketch of the model being shifted; in most cases, b₀ = l₀ = 0. Bottom: sketch of the LOS grid covering the projection of a model (red) with the weighting along a single LOS (blue): some cells (grey) are not taken into account because their centres are outside the LOS, while all cells inside the LOS with a common distance from the model centre share the same weight (coloured tiling patterns).