Problems with importing motion capture data can be very frustrating. The most common errors are connected with an inappropriate T-POSE of the BVH rig. This T-Pose depends on the software the animation was recorded in and exported from. Additionally, BVH rigs can have arbitrary bone hierarchies, with more than two spine bones for instance. A proper Unity Humanoid rig hierarchy was covered in the Configuring Generic and Humanoid rigs recipe in Chapter 1, Working with animations.

In Blender, the Rigify rig has a proper T-Pose. Thus, the best solution is to retarget the animation from the ImportRig to the FinalRig (the Rigify one). In theory, we could omit creating the control rig (the empties) but those give us more control. The (...)Target empties are not constrained to the ImportRig bones—they are only parented to the empties that are constrained. This way we can rotate or move the (...)Target empties to correct any rotation errors or adjust a pose.

We also use Inverse Kinematics for the feet in this setup. This, combined with the Offset option in the Copy Location constraints (set for the footTarget.L, footTarget.R, and hips bones), allows us to adjust the feet and hips positions. This way we can move the character to the center of the scene quite easily. We can even make it crouch while moving.