“…In order to overcome this difficulty we have to keep the extracted paths at a certain distance from the spatio-temporal cell boundaries or, in other words, they should be more centered inside the 4D segmentation. This can be achieved by using the constrained distance function D B (x 1 , x 2 , x 3 , θ) [15,1,17] values of which grow from boundaries to the center of the 4D spatio-temporal trees, see Fig. 8 right.…”