ampertox (11/27/2021)
@Peter, such bones alignment for a T-Pose cannot be done programatically, ie a button for the end user? Bottom line, it's pretty mathematical, lol, coordinates, therefore suitable for such tool.
Unfortunately it is virtually impossible. There is no standard armature structure and bones naming convention. It would vary from one source to another.
If you are lucky, a T-pose would be the at the first frame of the motion. If not, then little extra work would require.
But setting up a T-pose in 3D Exchange from some odd pose is no joy at all and is unnecessary.
Good news is that motions have a rest pose which is not visible in 3DX (very unfortunate).
So the goal is to extract that rest pose. Rest pose is set to T-pose most of the time (or at least to some sort of symmetrical pose, which is easy to convert to a T-pose, even in 3DX).
Easiest way is go through Blender. This has to be done only once for the set of motions you acquired from a specific vendor.
* Import one of the acquired BVH file into Blender
* Go to Object Data Properties (an icon with running human) and switch to the Rest Pose
* If you are in luck, then the pose would be a T-pose. If not, it would still be some sort of symmetrical pose, which is easy to tweak to a T-pose in Edit mode.
* Switch to Pose Mode. Ctrl+A > Apply Pose as Rest Pose (if you tweaked it in Edit Mode).
* Export as BVH, frames 1 to 1
* Open exported pose in 3DX, set X rotation to 270 and convert to Non-Standard
* Save T-pose and 3DX profiles
* Finally load motions one by one and use 2 saved profiles (T-pose and 3DX) to convert them to iMotion.