Fig 2. Angles and lengths characterizing the relative position of two fish.
Angle ψj denotes the angular position of fish Fj with respect to the horizontal (positive values fixed in the anticlockwise direction); angle ϕi is the heading of fish Fi; θwi is the angle of incidence of fish Fi with respect to the outer wall; dij is the distance between Fi and Fj; θij is the viewing angle of Fi with respect to Fj (not necessarily equal to θji), and ϕij = ϕj − ϕi is the heading difference of Fi with respect to Fj.