Add Lock Hips, Lock Head, Lock Both. Further musings on the influence of auto calibration spheres.

[CMC-Git-Report]

Is your feature request related to a problem?

Of the issues related to IK known so far, the next issue is how the spine & head work. I do not know the specifics of how the head, neck, and spine work on Avatars in Unity, VRC, or Basis, or any social platform.

I do know in VRC, the three noted options are presented in the small menu under IK. Each option works differently depending on the rigging of an avatar, the tracking method used, as the number of trackers used, the different proportions of the human body, and the diversity of bodies in general. Options are always good.

Here's how VRChat presents these options: https://docs.vrchat.com/docs/ik-20-features-and-options

From my experience as a Tundra/Lighthouse user who dances, lock Head allows for the hips, spine, and chest to more freely move independently from the head. The effect amplifies the more trackers are added (along with programs like Hai's).

Form my observations between VRChat and Basis, Basis VR appears to use IK visually similar to Lock Both. Unfortunately, I do not know this for sure, as I am unfamilair with the methodology of IK in general the code regarding its implementation in Basis.

In VRChat, Lock both has the side effect of causing the avatars leg movement to egregiously influence the spine of avatars as a general rule of thumb on 8+2 Tundra light house. The results on other tracking methods with different tracker/point amounts can differ.

An example of this lock both behavior would be standing with your left leg raised and tucked close to your body. The spine of the avatar may curve unpredictably but usually curves to the direction of the lifted leg (in this case, to the rightmost direction).

There is also a secondary issue, in that the current auto calibration of spheres doesn't give you control over Tracker ID, POINTS, or body parts selection. A second calibration sphere meant for the hip can accidentally attach to a leg bone. This not only influences spine curvature but also the IK of the leg directly, snapping it around 180 degrees. There is also the possibility that for the currently 15 available points in Basis there is no way to assign two trackers to the same body part based on auto calibrated proximity, but I would need more time to experiment (and would need a definitive answer on this aspect).

The calibration sphere issue is covered more here (#483) and tracker ID & point assignment issues here (#503)

Describe your preferred solution

Added options on the calibration menu for Lock Hips, Lock Head, or Both. The default should be changed to lock hips. If there are other lock options possible, they could be explored.

Describe any considered alternatives

.

Additional Context

I might need time to present picture or video related evidence. Due to the variability of the topic, should this topic be investigated as a group effort?