One objective of this system was to show that 3D visual tracking of a flying object is possible without making strong assumptions on the environment and using only off-the-shelf components like a PC (Pentium II/300MHz) and standard video cameras and framegrabbers with a frame rate of 50Hz.
In our general setting, the ball is in the air for about 0.8s to 1s, covering a distance of about 5m.This is just long enough for the robot to reach a typical catch point. Therefore it is essential to provide an early prediction of the trajectory to quickly command the catch position to the robot. As the ball is tracked for a longer time, the prediction becomes increasingly precise and the robots destination is modified. Therefore we put a stereo camera system with a quite large baseline of ca. 1m near the thrower and get this way a good prediction of the position and velocity of the ball after the first two frames from the cameras.