Depth estimation using the compound eye of dipteran flies

In the neural superposition eye of a dipteran fly every ommatidium has eight photoreceptors, each associated with a rhabdomere, two central and six peripheral, which altogether result in seven functional light guides. Groups of eight rhabdomeres in neighboring ommatidia have largely overlapping fields of view. Based on the hypothesis that the light signals collected by these rhabdomeres can be used individually, we investigated the feasibility of estimating 3D scene information. According to Pick (Biol Cybern 26:215-224, 1977) the visual axes of these rhabdomeres are not parallel, but converge to a point 3-6 mm in front of the cornea. Such a structure theoretically could estimate depth in a very simple way by assuming that locally the image intensity is well approximated by a linear function of the spatial coordinates. Using the measurements of Pick (Biol Cybern 26:215-224, 1977) we performed simulation experiments to find whether this is practically possible. Our results indicate that depth estimation at small distances (up to about 1.5-2 cm) is reasonably accurate. This would allow the insect to obtain at least an ordinal spatial layout of its operational space when walking.