title_body: Are these methods of Drone Localization Techniques for a dark environment plausible? I am working on a project where I need a quadcopter to accurately know its location relative to a starting point in a GPS denied environment in the dark.
  A quick overview of the project:
  
  The drone will be mounted on a vehicle in a docking station
  When prompted, the drone must hover above the vehicle by ~30 m
  The drone must be able to accurately locate its position relative to the docking station in the dark without GPS
  The drone must also be able to react to the movement of the vehicle (very small movements in nature)
  When finished, the drone will return to the docking station
  
  Given the requirements of the problem I have been looking at a couple of solutions:
  
  Use around 3 infrared beacons on different parts of the vehicle with a camera on the drone to perform localization (looking at the IR-LOCK sensor and beacons for this purpose)
  Use ultra-wideband communication with a similar setup of three or so anchors and one receiver on the drone (looking at the Pozyx anchors and tag)
  Use Bluetooth of some sort (haven't looked into this one as much)
  
  Any suggestions or tips you may have would be greatly appreciated. My main concerns are the range/feasibility of each option.
upvoted_answer: With sufficiently accurate and stable IMUs (think ADIS 164xx) on both vehicle and drone you should be able to calculate the relative offset between the two. In any way this will have to be a custom solution.
  What GPS denied environment are you referring to?