The Oculus Rift DK2 virtual reality headset uses an IR camera in conjunction with built-in accelerometer/gyro/magnetometer for accurate head/motion tracking. The previous version (DK1) used only an IMU device and had less accurate head-tracking and suffered from drift errors.
Why are current IMU devices (accelerometers, gyros etc) unable to accurately measure motion? What limitations exist with these devices and why? I understand gyros are accurate over short time scales, but have drift errors over larger times and require an accelerometer or magnetometer to correct this drift. Whereas accelerometers are unprecise over short durations of time and require averaging functions to output meaningful data.
Also, would it be possible to use multiple IMU devices in specific geometric locations to get more accurate and faster motion data? Regarding head-tracking, what other solutions are there using IMU devices (with shortest delay possible being the key factor in design)?