Acquire 3d position of object tracked with stereo cameras

Hi,

If you are using stereo cameras then disparity maps is the way to go. Depth cameras (like Kinect) would be an alternative,.

To start on disparity maps here is a good guide using OpenCV ( OF has a nice wrapper ) : http://docs.opencv.org/master/d9/db7/tutorial_py_table_of_contents_calib3d.html#gsc.tab=0

Then I suggest that, as you are only interested in the pingpong ball, you run an object detection algorithm to compute the disparity map only on the pixels for the object. If the background is still then a background / foreground detection + color detection for the ping pong ball will do.