Approach speed and path shape perceived intent
Aliases: trajectory legibility · approach kinematics · motion intent
What it is
Approach trajectory legibility is the degree to which path shape and velocity profile let an observer infer whether a robot will engage them, pass, yield, or travel elsewhere. Several trajectories can reach the same goal, but reactions depend on how early the motion removes ambiguity, not only on final separation.
Why it happens
Observers extrapolate heading, curvature, acceleration, and braking onset into future occupancy. Motion aimed at the body centre while accelerating supports a collision prediction; early deviation or deceleration supports passing or yielding. A shortest path may point both to a person and to a goal behind them, preserving ambiguity and making the person move unnecessarily early.
Studying it
Path curvature, peak speed, braking onset, and passing side can be varied with destination held constant. Frame-wise goal predictions, identification time, avoidance onset, path conflict, and discomfort reveal distinct effects. Geometry and kinematics must be controlled separately. Virtual stimuli support screening, but embodied avoidance still requires physical-space trials.
Where it stops holding
Legibility cannot compensate for excessive speed or inadequate braking. Crowding, occlusion, and multiple possible addressees make intent harder to resolve, while passing-side conventions vary. When a task demands a short path, an explicit preview may need to compensate for reduced kinematic readability.
Applying it
- Introduce visible deviation or braking before a human-intersection zone rather than swerving at close range.
- Detect early headings compatible with both the person and a goal behind them; add orientation or signalling if ambiguity persists.
- Ask untrained observers to mark when the destination becomes clear while recording avoidance and near misses. This exposes efficient but unreadable paths.