[Bug] 3D Body Tracking Accuracy Issue

[shiroii03]

Unity bug report case number
IN-80648

Describe the bug
Hi, I planned to use the ARkit3D body tracking to make an AR virtual cloth fitting app, but I discovered that the Human Body Tracking 3D is not accurate enough. The 3D body mesh from the sample will be offset from the camera input like the screenshots below.

I tested it with both a real person and pictures of a person, both behaved the same. I used the 5.1 and 6.0 versions of sample projects from this repo, and also the sample project from Apple https://developer.apple.com/documentation/arkit/arkit_in_ios/content_anchors/capturing_body_motion_in_3d. Not sure if this is the limitation of the AR foundation or hardware, or I overlooked something.

To Reproduce
Steps to reproduce the behavior:

1. Go to the sample project's HumanBodyTracking3D sample scene.
2. Run the scene.

Expected behavior
The 3D body mesh should align more accurately with the camera input.

Actual behavior
The 3D body mesh has offset on the arms and legs, causing it can't align properly with the camera input.

Smartphone (please complete the following information):

• Device: iPhone 12 Pro Max
• OS: iOS 17.5.1

Unity and AR foundation

• Unity 2022.3.15 and 6000.0.8
• AR Foundation 5.1 and 6.0