Timetocontact

Time-to-contact (TTC) is a perceptual and computational metric that estimates how long it will take for an observer to reach a collision with a moving object, assuming current relative motion continues. In human perception, TTC is obtained from visual information such as looming expansion and relative motion. In engineering, TTC is used as a collision-avoidance signal in robotics, autonomous vehicles, and simulation.

In simple kinematic terms, TTC can be computed as the distance to the object divided by the relative speed toward it (TTC = D/Vrel). More generally, observers rely on dynamic cues such as the rate of optical expansion (tau, or τ) to infer time to contact without knowing actual distance. Tau is the perceived time remaining for contact based on how rapidly the image of the object grows on the retina. These cues are sensitive to acceleration and occlusion.

Applications of TTC are widespread. In driving and piloting, TTC informs braking and avoidance decisions. In sports, athletes exploit TTC to time jumps, catches, or hits. In robotics and computer vision, TTC or time-to-collision metrics guide autonomous navigation and obstacle avoidance. In all uses, the assumption of constant velocity and straight-line motion is a limitation.

History and related concepts: The study of TTC grew from ecological psychology and studies of motion perception, with tau theory highlighting the importance of optical cues for timing actions. Related topics include optical flow, time-to-contact in navigation, and collision avoidance algorithms.