Algorithm 1 Distance calculation for the moving capsule.

Input: Absolute position ${\mathbf{P}}_{\mathbf{i}}=(x_i,y_i,z_i)$ Output: Moving distance L 1:set $flag=0$ 2:set $L=0$ 3:repeat 4: Get absolute position ${\mathbf{P}}_{\mathbf{i}}$ 5: if $\left|{\mathbf{P}}_{\mathbf{i}}-{\mathbf{P}}_{\mathbf{i}-\mathbf{1}}\right|\ge 4$ mm then 6:  Estimate adjacent moving angle $\theta$ 7:  if $\theta \in \left[{150}^{\circ },{210}^{\circ }\right]$ then 8:   $flag=flag\oplus 1$ 9:  end if 10:  Quadratic Bézier curve-fitting 11:  $distance={\int }_{{\mathbf{P}}_{\mathbf{0}}}^{{\mathbf{P}}_{\mathbf{2}}}{\mathbf{B}}_{\mathbf{t}}dt$ 12:  $L=L+distance\times {(-1)}^{flag}$ 13: else 14:  ${\mathbf{P}}_{\mathbf{i}}$ = ${\mathbf{P}}_{\mathbf{i}-\mathbf{1}}$ 15: end if 16:until Tracking End 17:returnL