Technical note: Out‐of‐plane angular correction based on a trigonometric function for use in two‐dimensional kinematic studies

In two‐dimensional (2D) kinematic studies, limb positions in three‐dimensional (3D) space observed in lateral view are projected onto a 2D film plane. Elbow and knee‐joint angles that are less than 20° out‐of‐plane of lateral‐view cameras generally exhibit very little measurable difference from their 3D counterparts (Plagenhoef 1979 Environment, Behavior, and Morphology; New York: Gustav Fisher, p. 95–118). However, when limb segment angles are more than 20° out‐of‐plane, as is often the case in locomotor studies of arboreal primates, elbow and knee angles can appear significantly more extended than they actually are. For this reason, a methodology is described that corrects 2D out‐of‐plane angular estimates using a series of trigonometric transformations. Am J Phys Anthropol, 2006. © 2005 Wiley‐Liss, Inc.