Is the tracker on the HMD 6DOF or 3DOF orientation? Either way, to integrate HMD tracking you should just need to use the
<link>.preMultLinkable command. After you have setup the link between the car and the viewpoint, just add the following code:
Code:
view_link.preMultLinkable(tracker)
The HMD tracker data should now be applied relative to the car orientation.