Main Page → Skeleton Tracking → 6 RigidBody Skeleton Markerset
This page provides instructions on how to set up and use the 6-Rigid Body skeleton markerset for full-body skeleton tracking. This guide is applicable to using the active pucks only.
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 estimates and 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 joint centers.
Let's first start with defining a rigid body for the chest puck. Open up the Trackables pane, make sure the Rigid Bodies option is selected at the bottom, and access the Create tab. This will bring up options for defining rigid bodies in Motive.
In the 3D viewport, select all of the 8 markers on the chest puck, and you should be able to see the selected markers in the Trackables pane. Name the rigid body as Chest, and click create. If you are attaching the active puck on the lower back, you will name the rigid body Hip instead.
Only either one of the Chest or the Hip rigid body is needed for the 6 rigid body skeleton.
Once the chest or hip rigid body has been created, the next step is to position and orient its pivot point at the appropriate location. You can use the Gizmo tool to easily translate the rigid body pivot points.
For the chest rigid body, the pivot point must be placed at the center of the torso, approximately at the heart center; which is in between the spine and the bottom end of the sternum. For the hip rigid body, the pivot point must be placed at the center of the hip bone.
After positioning the pivot point, adjust the orientation of the rigid body pivot also by using the rotate Gizmo tool. For creating 6 Rigid Body skeleton, the +z axis must direct towards the front of the actor.
Enabling the Orientation setting under the rigid body properties will reveal the orientation of the selected rigid body.
Now that the chest, or hip, is set up, next step is to set up the head rigid body. This can be either the HMD (HMDHead) if you are using the active CV1 clip, or simply an active puck attached to the head (Head). Only one of them needs to be created.
To create the HMD rigid body, you can use the HMD calibration tool in the Trackables pane to easily create a rigid body for the active CV1 clip. Make sure to choose either the +Z-forward or the +X-forward orientation when creating the rigid body, and it must be named HMDHead for +Z-forward orientation or HMDHeadX for +X-forward orientation.
The process of creating a head rigid body from an active puck is similar to the steps for creating the Chest rigid body. You can use the Trackables pane to define a rigid body named Head.
Once the rigid body is defined, use the Gizmo tool to translate the pivot point to at the center of the actor's head near the neck joint. Then, likewise, orient the rigid body so that +z axis is directing towards the front.
Now that the head and torso rigid body has been prepared, we can start defining the skeleton. Open the Trackables pane and select desired Rigid Body Skeleton from the marker set drop-down menu, and assign a name for the skeleton that will be created.
Ask the subject to strike a calibration pose (e.g. T-Pose). Then select the two rigid bodies and press Create on the Skeleton pane. This action will automatically define rigid bodies for the remaining active pucks on the hand/foot, and also place the pivot points at the proper location automatically. All of the rigid bodies will have the prefix with the name given to the skeleton (see screenshot below), and the skeleton will be created and tracked.
Rigid Body Names: