An XVS would consist of external sensors, primarily video imagery, which is provided to the pilot(s) in real time via one or more displays intended to augment or replace the windscreen.
Both EVS and SVS are primarily intended to improve situational awareness of the flight deck crew, especially at night and in poor visibility weather conditions such as rain, snow, fog, or smoke.
XVS is different in that it is intended to provide the flight deck crew a real time view of the outside world in visual meteorological conditions (VMC).
The solution on the Concorde was to have an articulating nose that drooped, exposing larger windows and allowing the pilots a better view during taxi, takeoff, approach, and landing.
[2] In 2008, following the Quiet Spike supersonic research program, NASA and Gulfstream again collaborated on an XVS flight demonstration program using NASA's TF-18 flight test aircraft[3][4] using commercial off-the-shelf High Definition video cameras and video displays while artificially restricting the aft seat pilot's view of the outside world.