Keeping Groups Coherent while Following a Path

Abstract

Keeping groups coherent while they are following a path is an important aspect of e.g. real-time strategy games. In these games, a lone character wandering off without the cover of its companions is often a lost character. In addition to guaranteeing coherence, planning the path for a group should be possible in real-time for large groups of characters and should look visually convincing.

In this paper, we describe a new method for keeping groups coherent while following a path, which meets these requirements. The running time of this method is O(n), where n is the number of characters. The method requires a path as input, represented by a set of connected line segments. It then constructs multiple displaced paths, called lanes, around the input path. Characters are equally divided over these lanes. When the available space around the input path changes, so does the number of lanes that fit. When this happens, the characters are redistributed over the available lanes.

Coherence is enforced by limiting the lateral and longitudinal dispersion of the group. The former is controlled by setting a maximum number of lanes, which is a parameter. The later is dynamically limited using the perfect ordering of characters on the lanes, which is the ordering where all characters are exactly their preferred distance away from each other.

Experiments show it yields visually convincing paths and coherent groups in real-time. Our method stands out because the motion of the characters is visually more convincing than other methods, and it has no oscillations.