I'm trying to get a 6DOF pose solution for an object that'll be between 10 and 50 cm from a fixed point. I want to avoid putting too much special hardware on the object, but extra hardware on the fixed side is fine.
I've been looking into two general methods:
fiducial markers There are several software packages with different types of markers, but I haven't been able to find any information about them regarding precision or accuracy in short-range pose sensing.
ultrasonics I've found some commercial systems that do 6DOF pose sensing (e.g. hexamite), but they're expensive and require you to put transmitters on the object.