C Specification

This extension defines 70 joints for body tracking: 18 core body joints + 52 hand joints.

// Provided by XR_FB_body_tracking
typedef enum XrBodyJointFB {
    XR_BODY_JOINT_ROOT_FB = 0,
    XR_BODY_JOINT_HIPS_FB = 1,
    XR_BODY_JOINT_SPINE_LOWER_FB = 2,
    XR_BODY_JOINT_SPINE_MIDDLE_FB = 3,
    XR_BODY_JOINT_SPINE_UPPER_FB = 4,
    XR_BODY_JOINT_CHEST_FB = 5,
    XR_BODY_JOINT_NECK_FB = 6,
    XR_BODY_JOINT_HEAD_FB = 7,
    XR_BODY_JOINT_LEFT_SHOULDER_FB = 8,
    XR_BODY_JOINT_LEFT_SCAPULA_FB = 9,
    XR_BODY_JOINT_LEFT_ARM_UPPER_FB = 10,
    XR_BODY_JOINT_LEFT_ARM_LOWER_FB = 11,
    XR_BODY_JOINT_LEFT_HAND_WRIST_TWIST_FB = 12,
    XR_BODY_JOINT_RIGHT_SHOULDER_FB = 13,
    XR_BODY_JOINT_RIGHT_SCAPULA_FB = 14,
    XR_BODY_JOINT_RIGHT_ARM_UPPER_FB = 15,
    XR_BODY_JOINT_RIGHT_ARM_LOWER_FB = 16,
    XR_BODY_JOINT_RIGHT_HAND_WRIST_TWIST_FB = 17,
    XR_BODY_JOINT_LEFT_HAND_PALM_FB = 18,
    XR_BODY_JOINT_LEFT_HAND_WRIST_FB = 19,
    XR_BODY_JOINT_LEFT_HAND_THUMB_METACARPAL_FB = 20,
    XR_BODY_JOINT_LEFT_HAND_THUMB_PROXIMAL_FB = 21,
    XR_BODY_JOINT_LEFT_HAND_THUMB_DISTAL_FB = 22,
    XR_BODY_JOINT_LEFT_HAND_THUMB_TIP_FB = 23,
    XR_BODY_JOINT_LEFT_HAND_INDEX_METACARPAL_FB = 24,
    XR_BODY_JOINT_LEFT_HAND_INDEX_PROXIMAL_FB = 25,
    XR_BODY_JOINT_LEFT_HAND_INDEX_INTERMEDIATE_FB = 26,
    XR_BODY_JOINT_LEFT_HAND_INDEX_DISTAL_FB = 27,
    XR_BODY_JOINT_LEFT_HAND_INDEX_TIP_FB = 28,
    XR_BODY_JOINT_LEFT_HAND_MIDDLE_METACARPAL_FB = 29,
    XR_BODY_JOINT_LEFT_HAND_MIDDLE_PROXIMAL_FB = 30,
    XR_BODY_JOINT_LEFT_HAND_MIDDLE_INTERMEDIATE_FB = 31,
    XR_BODY_JOINT_LEFT_HAND_MIDDLE_DISTAL_FB = 32,
    XR_BODY_JOINT_LEFT_HAND_MIDDLE_TIP_FB = 33,
    XR_BODY_JOINT_LEFT_HAND_RING_METACARPAL_FB = 34,
    XR_BODY_JOINT_LEFT_HAND_RING_PROXIMAL_FB = 35,
    XR_BODY_JOINT_LEFT_HAND_RING_INTERMEDIATE_FB = 36,
    XR_BODY_JOINT_LEFT_HAND_RING_DISTAL_FB = 37,
    XR_BODY_JOINT_LEFT_HAND_RING_TIP_FB = 38,
    XR_BODY_JOINT_LEFT_HAND_LITTLE_METACARPAL_FB = 39,
    XR_BODY_JOINT_LEFT_HAND_LITTLE_PROXIMAL_FB = 40,
    XR_BODY_JOINT_LEFT_HAND_LITTLE_INTERMEDIATE_FB = 41,
    XR_BODY_JOINT_LEFT_HAND_LITTLE_DISTAL_FB = 42,
    XR_BODY_JOINT_LEFT_HAND_LITTLE_TIP_FB = 43,
    XR_BODY_JOINT_RIGHT_HAND_PALM_FB = 44,
    XR_BODY_JOINT_RIGHT_HAND_WRIST_FB = 45,
    XR_BODY_JOINT_RIGHT_HAND_THUMB_METACARPAL_FB = 46,
    XR_BODY_JOINT_RIGHT_HAND_THUMB_PROXIMAL_FB = 47,
    XR_BODY_JOINT_RIGHT_HAND_THUMB_DISTAL_FB = 48,
    XR_BODY_JOINT_RIGHT_HAND_THUMB_TIP_FB = 49,
    XR_BODY_JOINT_RIGHT_HAND_INDEX_METACARPAL_FB = 50,
    XR_BODY_JOINT_RIGHT_HAND_INDEX_PROXIMAL_FB = 51,
    XR_BODY_JOINT_RIGHT_HAND_INDEX_INTERMEDIATE_FB = 52,
    XR_BODY_JOINT_RIGHT_HAND_INDEX_DISTAL_FB = 53,
    XR_BODY_JOINT_RIGHT_HAND_INDEX_TIP_FB = 54,
    XR_BODY_JOINT_RIGHT_HAND_MIDDLE_METACARPAL_FB = 55,
    XR_BODY_JOINT_RIGHT_HAND_MIDDLE_PROXIMAL_FB = 56,
    XR_BODY_JOINT_RIGHT_HAND_MIDDLE_INTERMEDIATE_FB = 57,
    XR_BODY_JOINT_RIGHT_HAND_MIDDLE_DISTAL_FB = 58,
    XR_BODY_JOINT_RIGHT_HAND_MIDDLE_TIP_FB = 59,
    XR_BODY_JOINT_RIGHT_HAND_RING_METACARPAL_FB = 60,
    XR_BODY_JOINT_RIGHT_HAND_RING_PROXIMAL_FB = 61,
    XR_BODY_JOINT_RIGHT_HAND_RING_INTERMEDIATE_FB = 62,
    XR_BODY_JOINT_RIGHT_HAND_RING_DISTAL_FB = 63,
    XR_BODY_JOINT_RIGHT_HAND_RING_TIP_FB = 64,
    XR_BODY_JOINT_RIGHT_HAND_LITTLE_METACARPAL_FB = 65,
    XR_BODY_JOINT_RIGHT_HAND_LITTLE_PROXIMAL_FB = 66,
    XR_BODY_JOINT_RIGHT_HAND_LITTLE_INTERMEDIATE_FB = 67,
    XR_BODY_JOINT_RIGHT_HAND_LITTLE_DISTAL_FB = 68,
    XR_BODY_JOINT_RIGHT_HAND_LITTLE_TIP_FB = 69,
    XR_BODY_JOINT_COUNT_FB = 70,
    XR_BODY_JOINT_NONE_FB = -1,
    XR_BODY_JOINT_MAX_ENUM_FB = 0x7FFFFFFF
} XrBodyJointFB;

Description

The backward (+Z) direction is parallel to the corresponding bone and points away from the finger tip. The up (+Y) direction is pointing out of the back of and perpendicular to the corresponding finger nail at the fully opened hand pose. The X direction is perpendicular to Y and Z and follows the right hand rule.

The wrist joint is located at the pivot point of the wrist, which is location invariant when twisting the hand without moving the forearm. The backward (+Z) direction is parallel to the line from wrist joint to middle finger metacarpal joint, and points away from the finger tips. The up (+Y) direction points out towards back of the hand and perpendicular to the skin at wrist. The X direction is perpendicular to the Y and Z directions and follows the right hand rule.

The palm joint is located at the center of the middle finger’s metacarpal bone. The backward (+Z) direction is parallel to the middle finger’s metacarpal bone, and points away from the finger tips. The up (+Y) direction is perpendicular to palm surface and pointing towards the back of the hand. The X direction is perpendicular to the Y and Z directions and follows the right hand rule.

Body skeleton has the full set of body joints (e.g. defined by XrBodyJointFB), organized in a hierarchy with a default T-shape body pose.

The purpose of the skeleton is to provide data about the body size. Coordinates are relative to each other, so there is no any relation to any space.

The calculation of the body size may be updated during a session. Each time the calculation of the size is changed, skeletonChangedCount of XrBodyJointLocationsFB is changed to indicate that a new skeleton may be retrieved.

See Also

XR_FB_body_tracking

Document Notes

For more information, see the OpenXR Specification

This page is extracted from the OpenXR Specification. Fixes and changes should be made to the Specification, not directly.

Copyright

Copyright 2014-2024, The Khronos Group Inc.

This work is licensed under a Creative Commons Attribution 4.0 International License.