Step 2. When using CPM, first the effective values of J, and P and λ p in 2D, or S and λ s in 3D, have to be determined, or inversely the correct values of $$J_{_{\mathit {CPM}}}$$ etc. have to be assigned. This is done by calculating the perimeter scaling factor ξ, which depends on the neighbourhood radius, in its turn depending on the neighbourhood level. The value of ξ can be obtained either by using the theoretical formulae Eq. 29, Eq. 33, for 2D and 3D respectively, in the case that the neighbourhood is sufficiently large, or by using the numerical estimates given in Table 2, for small neighbourhoods that can present significant deviations from those theoretical values. Transformations between the effective and CPM parameter values are then given by Eq. 31, Eq. 32 for 2D, and Eq. 34 for 3D. Note that because of the way interfacial tension is implemented in the CPM, $$J=\xi J_{_{\mathit {CPM}}}$$ for cell-medium interfaces and $$\frac {\xi }{2}J_{_{\mathit {CPM}}}$$ for cell-cell interfaces.