Dear Chio, thanks for your questions.
I trust this will develop into a very useful thread about AdonisFX and MetaHumans.
1. Layering Strategy: In AdonisFX, what is the recommended order for simulating the deep muscles (Subscapularis, Infraspinatus, Teres Minor) vs. the superficial layers (Trapezius and Deltoid)? Should I use AdnFascia between the scapula and the ribcage to prevent penetration?
In production the most usual approach is to simplify the anatomy. This means that most of the deep muscles are usually not modelled and simulated; you may fill that gap with the volume of the superficial muscles or emulate those internal volumes with geometries that represent multiple deep muscles in a single mesh. The same way, there is a trend to simplify also the skeleton geometry, where areas like the scapula are modelled as contiguous geometries. This simplifies the simulation setup, accelerates the processing and prevents popping and aberrations.
If you are looking at a perfectly anatomical simulation and result, let me know and I will recalibrate my answer more towards brute-force accuracy and less towards efficiency.
2. Sensor Placement: Which MetaHuman joints are best suited for driving the AdnSensors for the rotator cuff? Should I target the upperarm_l rotation, or the scapula_l translation?
My approach is to think about sensors by listing themain actions of the desired muscle (or group of muscles).
The rotator cuff is a group of 4 muscles including: supraspinatus, infraspinatus, teres minor, and subscapularis.
supraspinatus: arm abduction
infraspinatus: external rotation
teres minor: external rotation
subscapularis: internal rotation
This means you need three sensors (see image below):
arm abduction: distanceSensor red line
external rotation: distanceSensor blue line
internal rotation: distanceSensor green line
3.Collision Handling: How do you manage the tight space between the humeral head and the acromion? I often encounter jittering when the arm is in full abduction (raised high).
This issue is typically resolved by modeling the skeleton as a contiguous surface where there is no actual gap between the humeral head and the acromion. This also applies to the gap between the scapula and the ribcage.
4. MetaHuman Helpers: Do you recommend using the MetaHuman “shoulder helper joints” as additional influences for the AdnMuscle nodes to maintain volume?
This is not strictly necessary, however if you want the muscles to closesly emulate the deformation behavior of the metahuman skin, you may indeed use those joints to help drive the shape of the muscles. However, keep in mind that the more influences you add to an AdnMuscle solver, the harder it will be to paint the attachment maps to direct the results.
I hope this helped you. I will also prepare some snapshots and post them in another reply tomorrow as i am sure it will help further clarify ideas.
