Figure 6.

POG construction. Symbols inside the circles are the aligned node IDs. The table associated with each node encodes the set of points aligned to it. In particular, each row represents a point with its trajectory ID (T column) and its index along the trajectory (S column). For example, the entry (1, 2) associated with node b in (a) means that the aligned node b currently include the point $p_2^1$, the second point from trajectory-1. In (a), a POG is initialized by the trajectory T₁. An example of a POG after aligning a few trajectories is shown in (b). Note that a new node/branch is created when a point cannot be aligned to any existing nodes. For example, node e was created when $p_3^2$ (i.e, the 3rd point of T₂) was inserted. (c) shows the POG after merging point $p_2^1$ from the node b to the node e constrained by the distance threshold ε.