Comparing geometric models for orientation: Medial vs. principal axes

Research examining the encoding of geometry for orientation has received considerable attention in the last 25 years with the proposition of a geometric module.1 Supporting the importance of geometry in the formation of a spatial representation, to date the majority of species studied show an encoding of geometry, even when presumably more salient and reliable features could be used. Although studies have shown that animals encode geometric information such as distance, direction or angular amplitude from the environment, few have tested the assumption that geometry is encoded using global properties such as the major principal axis, a strongly supported proposition. Here we present an alternative model to principal axis, specifically medial axis. In addition we describe the straight skeleton model, which may also offer insights into the understanding of geometric encoding by orienting animals.