Figure 6.

Locating airway wall point $p_s$. Green dot denotes the current surface point $p_i$, yellow dot denotes the candidate position $p_v$, red dot is the closest k-d tree point $p_s$ to $p_v$, cyan dot is the closest airway centerline point $p_l$ to $p_v$, and orange hollow dot is the correct surface voxel $p_s^{\prime }$.