3.1.1. The Kernel Elongation Parameter ρ

Figure 5 shows the TRE values of the FMIND method using different ρ values. For the purpose of evaluating the influence of ρ on registration accuracy, we have set the significant level α = 0.05 in one-way Analysis of Variance (ANOVA) [41]. The obtained significance value *P* is 0.001, which means that ρ has a significant impact on registration accuracy of the FMIND method. From Figure 5, we can see that the TRE achieves the minimum value when ρ = 2. Thus, we have fixed ρ = 2 in the proposed method.

**Figure 5.** The target registration error (TRE) with different ρ values.
