Glossary · Robotics and control
Occlusion
Also called line of sight, ray casting, blindness, occluded, hidden
When something is hidden from view because something else is in the way, such as your own arms in front of your eyes.
A point is occluded when it is out of sight because something solid is between it and the eye. In robotics it is one of the main ways a camera’s view is worse than a simulation’s: the simulation knows where everything is, the camera only sees what isn’t hidden.
A simple way to simulate it is ray casting: draw a straight line from the eye to the point and ask the physics engine whether the line hits anything first. If it does, the point is hidden. With two eyes, a point is hidden only if both lines are blocked.
What a policy does with a hidden point is a design choice. Here it keeps the last position it saw, its velocity is set to zero, and a flag says it is unseen. That is roughly what a person has: a memory of where the hand was, and no news of where it is going.
In this project
In the blocking post, rays go from both of the fighter’s eyes to each of the opponent’s 16 keypoints on every step, and the fighter’s own arms and body can block them. Against an opponent standing ahead, the stance guard sees 10 of 13 test points, the left high block 9, the right high block and the low front block all 13, and the front block, with both forearms in front of the face, none at all.
There is no reward term for “couldn’t see”. The cost of covering the eyes is meant to be what it costs a real fighter: the next punch arrives unseen. A penalty for blindness would first teach the fighter not to block at all.