>>295463203
Actually we can do more about this problem as long as we make a few assumptions and the user follows them. If the user has at least one foot in contact with the ground at all times, we can then work upwards from the foot. Basically your feet are anchored to the ground or frozen in their position. Then IK is used to figure out the position of your upper legs based on the rotation, and then the hips and spine. The user just needs at least one foot on the ground at any time in order for the IK to work. This is actually how some IMU-only systems do positional tracking by themselves, and it's proven to work. For instance, I think it was Xsens who demonstrated at a conference how someone could be tracked with very little drift using that method, where they walked around the conference and returned, and when then stepped back into the original location, their virtual avatar was only off by like a few cm.