Unlike real walls where movement is blocked in both directions the Wall entity is in fact a one-way barrier. It allows agents to pass through from the 'inside' to the 'outside' but not the other way. Therefore it is important to create the wall so that it is facing the right way.
A wall entity is created by specifying its end points (P0, P1). If the wall is rotated clockwise about the first point (P0) then it is passing in the direction of the wall normal and through the 'outside'.
To detect a wall invisible feelers (purple) extend from the agent. When one of these feelers intersect with the wall a steering force proportional to the penetration depth is applied to the agent in the direction of the wall normal.
The number of feelers, their length nd their field of view are all configurable.