Schematic figure of the truncated-pyramidal volume of the mock catalogue of a cluster extracted from the simulation. The solid dots show the positions of the dark matter particles in a slice of the simulation box centred on the cluster C. The orange (blue) dots are within (outside) the volume. This figure has only an illustrative purpose: the actual mock catalogues have b_L ≫ r_FOV and include a substantially larger number of particles than shown here.