Kernel function given by Eq. (13) for an ellipsoid with a = 1, b = 0.9, c = 0.6 at (θ, ϕ) ≈ (0.632,0.132), corresponding to a node of the Chebyshev grid, and for r = 1.001 s(θ, ϕ). The kernel, κ_ℓ, is plotted as a function of ϕ′ for θ′ = θ and zoomed-in on the lobe. The Chebyshev grid has N + 1 = 17 nodes. The dashed line corresponds to the Chebyshev approximation of the kernel, and the dashed-and-dotted line shows the kernel of the concentric and coincident sphere, corresponding to κ_ℓ,0 in Eq. (27).