I have seen built-in HUD in both a BMW and a Mini Cooper. In the first the windshield is used as the combiner while in the second they use a separate piece of glass located on the dashboard. The system work by reflecting and magnifying a real image to create a larger virtual image at some distance beyond the windshield. In both cases the virtual image appears to be projected close to the hood of the car, which would be 1m or 1.5m beyond the windshield.
Some head mounted displays (HMD) or near eye display (NED), for example, the Vuzix glasses claim that the virtual image is projected at infinity. How come a head mounted display which is so tiny can project the virtual image at infinity and a built-in HUD which is 10times bigger can’t project the image more than a couple of meters? Do you know if HMD have inherent advantages when projecting a virtual image far away related to the proximity of the optics to the pupil of the eye?