  In a crowd, individuals make different motion choices such as "moving to
destination", "following another pedestrian", and "making a detour". For the
sake of convenience, the three direction choices are respectively called
destination direction, following direction and detour direction in this paper.
Here, it is found that the featured direction choices could be inspired by the
shape characteristics of Voronoi diagram. To be specific, in the Voronoi cell
of a pedestrian, the direction to a Voronoi node is regarded as a potential
"detour" direction, and the direction perpendicular to a Voronoi link is
regarded as a potential "following" direction. A pedestrian generally owns
several alternative Voronoi nodes and Voronoi links in a Voronoi cell, and the
optimal detour and following direction are determined by considering related
factors such as deviation. Plus the destination direction which is directly
pointing to the destination, the three basic direction choices are defined in a
Voronoi cell. In order to evaluate the Voronoi diagram based basic directions,
the empirical trajectory data in both uni- and bi-directional flow experiments
are extracted. A time series method considering the step frequency is used to
reduce the original trajectories' swaying phenomena which might disturb the
recognition of actual forward direction. The deviations between the empirical
velocity direction and the basic directions are investigated, and each velocity
direction is classified into a basic direction or regarded as an inexplicable
direction according to the deviations. The analysis results show that each
basic direction could be a potential direction choice for a pedestrian. The
combination of the three basic directions could cover most empirical velocity
direction choices in both uni- and bi-directional flow experiments.
