6 Rigid Body Skeleton Markerset

Main PageSkeleton Tracking6 RigidBody Skeleton Markerset
New in Motive 2.0

Page Scope

This page provides instructions on how to use the 6-Rigid Body skeleton markerset for full-body skeleton tracking.

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The 6 Rigid Body skeleton feature is not exposed in Motive 2.0. To access this skeleton template, please contact our support.


Overview


The 6 Rigidbody Skeleton markerset allows users to use just rigid bodies to establish full body skeleton tracking. A total of six rigid bodies are attached at specific locations of the subject and Motive solves the entire skeleton through inverse kinematics. The rigid bodies are attached to the head, left-hand, right-hand, hip, left-foot, and right-foot, and then the pivot point of those rigid bodies needs be translated over to the corresponding joints.

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Creating 6RB skeleton markerset


Marker Placements

Step 1) Prepare 6 rigid bodies with markers.

Step 2) Attach rigid bodies at the following locations:

  • Head: Place the rigid body back of the head. This can be replaced by an HMD.
  • Hip: Place the rigid body on the back, slightly above the hip bone.
  • Right Hand / Left Hand

Step 3) Make sure the rigid bodies are securely attached.

Creating the Skeleton

Example rigid body names for Actor skeleton.

Step 1

First of all, define rigid body assets for all of the attached rigid bodies.

Step 2

Name the rigid bodies with the following syntax:

  • (Skeleton Name)Head
  • (Skeleton Name)Hip OR (Skeleton Name)Chest
  • (Skeleton Name)LHand
  • (Skeleton Name)RHand
  • (Skeleton Name)LFoot
  • (Skeleton Name)RFoot

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The Hip rigid body can be replaced with a Chest rigid body if placing a rigid body on the waist is not possible.

Step 3

Now you need to position the rigid body pivot points. Use the Gizmo tool and translate the rigid body pivot points so that each pivot point is located at its respective parent joint axis. Pivot point of the head rigid body must be placed over the head/neck joints, the hip rigid body must have its pivot point at the pelvis center, pivot point of the left/right hand rigid bodies must be placed over the wrist joints, and the left/right foot rigid bodies must have its pivot points over the ankle joints, as shown in the image below. If a Chest rigid body is used in place of the Hip rigid body, its pivot point location need to be plated at the heart center, solar plexus.

Pivot Point Locations: Pivot: Head. Pivot: Left and Right Hand, Pivot: Left and Right Foot, Pivot: Hip (or replaced by Chest rigid body).

Step 4

Orient the rigid body pivot points so that all of its z-axis is facing in forward-direction. This can be done easily using the Rigid Body pane. Ask the subject to face towards the positive-z direction (determined by the global coordinate system) and use the Edit tab on the Rigid Body pane to reset the orientations of the each rigid body. This will align the rigid body orientation with the global coordinate axis, making the z-axis direct forward.

Reseting rigid body orientation

Step 5

Open the Skeleton pane and select the 6 Rigidbody Skeleton markerset. Name the skeleton that matches the prefix given to the rigid bodies.

Creating 6RB skeleton with skeleton name Actor

Step 6

Select all six rigid bodies and press "Create" on the Skeleton pane. Created skeleton will search for rigid bodies with corresponding names for tracking. If all of the rigid bodies have been named correctly and the pivot points have been positioned and oriented properly, the skeleton will be tracked.