Wiiheadtrack supports two modes:
The object-mode simulates the situation having an object in front of the user (e. g. on a table) and moving around the object. The movement is similar to the movement on the surface of a sphere, why the object-mode maps the user-position onto a sphere.
The room-mode simulates the user standing in a room, looking in the direction of the negative z-axis and moving in three dimensions (left/right, up/down, forward/backward). The movement is similar to the movement on a plane which moves forward/backward itself.