Headtracking while user is wearing HMD
Working on a VR project where it is necessary to get data about the user's body via a second, external, stationary webcam. Specifically, I'm looking to track chest-movements for breathing. It seems like normally an easy way to get the chest position is by extrapolating from face-tracking data. However, since the user will always be wearing an HMD (i.e. Morepheus, Oculus), this will likely interfere with things.
Any suggestions for the best method? Would just tracking the mouth be possible? I'm just using a standard webcam for the second camera, so Kinect-style skeletal tracking would be hard.
Thanks for the help in advance.]
EDIT: Doing research, it seems a lot of facetracking programs use Haar Cascades. Would it be possible/realistic to train a new Haar Cascade xml based on pictures of users wearing HMD's?
Maybe you could use an AR marker sticked to the HMD to get the head position ?
I'm hoping to be able to distribute it without any additional hardware beyond the Morpheus and PS4 camera, so this unfortunately wouldn't work although I've considered it.