For the clients in this article, the only path planning needed is the ability to steer along a straight line. Given a line and periodically its own position, the client's goal is to eventually be travelling precisely parallel to the line within a certain distance from the line. This distance, or the tolerance, is a parameter, but throughout this article it is set to 5 units. Since the agent's width is 20 units, this tolerance allows the client to strike the ball as expected.
The client begins by computing its distance from the line as well as its offset from the correct heading (the slope of the line). If the client's distance is greater than the tolerance, then the agent steers sharply towards the line. In particular, it sets its steering in proportion to its distance from the line minus the tolerance. If the distance is no more than the tolerance (or once it has become so), then the client steers towards the line with a force proportional to its heading offset. Thus, when the client is heading parallel to the line, its wheel is centered.
Although this method does not force the client to travel exactly along the given line, it does allow the client to be moving in precisely the right direction. Thus it is able to reliably strike the ball in a particular direction.