Normalization of the spherical kernel (Eq. (3)) as a function of the 3D radius r for three choices of binning in r and discretized values of s₁ and s₂. In red for a linear binning of Δr = 1; in blue for a linear binning of Δr = 3 and in green for a linear binning of Δr = 5. These normalizations are compared to the results of Eq. (3) in the case of continuous values of s₁ and s₂, in black. For better visibility, the normalizations for Δr = 1 and Δr = 3 have been multiplied by 100 and 10, respectively.