Figure 4
From: Infrared-based facial points tracking and action units detection in context of car driving simulator
Sliding of the normalized Euclidean distance curve to detect apex/antapex locations (see text for details). The antapex term here is used to express the difference between the apexes in two opposite directions. The neutral point corresponds to an absence of AU. The apex is reached from the neutral expression when it’s increasing and the antapex correspond to a Euclidien distance less than the neutral distance.