I noticed the other day that heads up displays in combat aircraft seem to have an accurate reticle regardless of the pilots head position and angle. It always seems to shoot the right way no matter what I do with my head. (Where as of course if I hold a rifle in real life, and move my head, the rifle's line of fire would no longer match up with where I am looking, which is why you need to line up the two sight markers to aim)
Can someone please explain to me the theory/method of how this works? Does the HUD somehow know which way the pilot is looking, and adjusts the symbology to offset the angle of the pilots head in real time?