Coordinate Frames

Wuji Glove is an intelligent data glove designed for robot teleoperation and human-computer interaction research, equipped with three sensor systems: tactile matrix, EMF spatial tracking, and IMU inertial measurement. To ensure seamless integration with the ROS ecosystem and robot control systems, Wuji Glove's coordinate frame design follows the ROS community standards REP-103, REP-120, and REP-155.

This document describes the coordinate frame conventions, axis orientation definitions, and frame tree structure of Wuji Glove.

Coordinate frame conventions

Right-hand rule

All coordinate frames in Wuji Glove follow the right-hand coordinate system (REP-103):

• Extend your right hand, curl your fingers from the X-axis toward the Y-axis — your thumb points in the Z-axis direction
• The same applies to rotations: the curl direction of your fingers is the positive rotation direction

Axis definitions

Body Root Node

REP-155 human body root frame. Origin at the midpoint between left and right hip joints. All skeletal joint frames are child nodes.

Wrist Node

Terminal node of the arm kinematic chain, serving as Wuji Glove's reference origin — all sensor frames on the glove are mounted under this node.

Frame tree structure

Full Body Frame Hierarchy

Wuji Glove's frame system follows the REP-155 human skeleton model, defining a complete kinematic chain from the body root node to the fingertips. The glove currently uses the arm chain portion (from wrist downward).

Frame definitions:

world                                       ← Root node
└── waist                                   ← Waist
    └── l_wrist / r_wrist                   ← Wrist ★
        ├── l_hand_emf_tx / r_hand_emf_tx   ← back-of-hand transmitter coil
        └── l_palm_imu_link / r_palm_imu_link ← Palm IMU

Nodes marked with ★ are the starting frames for the glove's actual data output.

Glove Sensor Frame Hierarchy

Below the wrist node, the glove mounts two child frames:

• emf_tx: back-of-hand transmitter coil frame, serving as the reference origin for EMF spatial tracking
• palm_imu_link: Palm IMU frame, used for orientation estimation

Both transforms are published via the tf_static data stream at 1Hz, with parent frame {l/r}_wrist.

Coil Coordinate Frames

Definition

EMF spatial tracking uses two types of coils:

• Back-of-hand transmitter coil: housed inside the back-of-hand module enclosure, corresponding to the emf_tx frame (published via tf_static at 1 Hz), serving as the reference origin for EMF spatial tracking.
• Finger receiver coils: one set embedded in each fingertip enclosure (5 sets total). These are not published as standalone frames; their positions are computed by EMF pose estimation (emf_poses) and reported in the emf_tx frame.

Both frame origins are located at the geometric center of the corresponding coil, with axis orientation identical to the parent frame (transmitter follows wrist; receivers follow the corresponding fingertip frame) — only a translational component exists relative to the parent, with no rotation.

Coil Position Parameters

The following measurements reference the right-hand design, with values rounded to account for manufacturing tolerances. From the wearer's perspective, with the hand naturally open:

Back-of-Hand Transmitter Coil

Finger Receiver Coil