Burrow-centric distance-estimation methods inspired by surveillance behavior of fiddler crabs

There are several ways to estimate the distance to an object based on visual information. Many robotic systems compute object distances based on disparity values or motion information. In addition to a disparity cue or image motion, research has shown that animals can possibly estimate the distance using the image size as well as the azimuth and elevation angles in their visual field. In this paper, inspired by the vigilance behavior of fiddler crabs, we suggest distance-estimation methods with several visual cues for engineering applications. A foraging fiddler crab can estimate the distance of an intruder from the burrow entrance. If the intruder is close to the burrow, the crab rushes back home to maintain possession of the burrow. In this study, we investigated burrow-centered distance-estimation methods based on visual information such as the retinal position, that is, the azimuth and elevation angles in an omnidirectional view as well as the image size and retinal speed of a target object. The methods show potential for engineering applications to the surveillance problem.