Difference between revisions of "Template:HMD Setup"

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<li style="display: inline-block; vertical-align: text-top;">[[Image:UEP_HMDside.png|thumb|410 px|Sample marker placement: Side view. The two side markers are aligned along the eye-level of the user.]]</li>
<li style="display: inline-block; vertical-align: text-top;">[[Image:UEP_HMDside.png|thumb|410 px|Sample marker placement: Side view. The two side markers are aligned along the eye-level of the user.]]</li>
==Oculus Positional Tracker (Rift sensors)==
<div style="padding-left:2em;">
When using an OptiTrack motion capture system to provide a solution for tracking Oculus HMD, avoid connecting its positional tracker, the Rift sensor, to the host PC.
When the tracker is connected, IR LEDs on the connected HMD will illuminate, and it could interfere negatively with the IR tracking of the motion capture system.  When Oculus tracker is not recognized by the computer, an error message may appear but you should be able to ignore the error message and proceed without the tracker.

Latest revision as of 22:34, 23 May 2019

HMD Tracking Setup

Setup and optimize the motion capture volume as explained in the Getting Started guide or the Hardware Setup documentations. If you plan to install any obstacles (e.g. walls) within the capture volume, make sure they are non-reflective, and place and orient the cameras so that every corner is thoroughly captured by multiple cameras. For typical rigid body tracking, attach the rigid body markers as instructed from the Rigid Body Tracking page. However, when tracking an HMD, extra attention to placing the markers is necessary.

HMD Marker Setup


When attaching retroreflective markers, make sure markers are securely attached and readily captured by the cameras. For attaching the markers, we recommend using our 20 mm wide and 30 mm tall M4 threaded plastic marker bases with Acrylic adhesives, available at the webstore, to attach the markers onto the HMD.


A markered HMD will be defined as a rigid body in Motive. When placing markers, make sure the placement asymmetry is respected in the arrangement within the HMD. Also, the marker arrangements between multiple HMDs must be incongruent. For more details, read about marker placement from the Rigid Body Tracking page. Also, for tracking the HMD, two landmark markers must be placed in the following locations:

Eye-level Side Markers (2)

Place two markers on left and right side of the HMD, these markers will serve two additional purposes. First, they will indicate yaw of the HMD, and they will be used to align the rigid body orientation with the orientation of the actual HMD component. Thus, a line interconnecting the two markers must be parallel to the frontal plane, or the display, of the HMD. Second, these markers will be used to locate the elevation of the eyes when creating the rigid body in Motive. In summary, the two landmark markers must be carefully placed considering the following:

  • The markers should align along eye-level of the user when the HMD is mounted.
  • Most importantly, place these markers in the exactly same location of the left and right side so that they form a precisely symmetrical arrangement.
  • Same dimension attachment bases must be used for both of the markers.

  • Sample marker placement: Front view. The two side markers are placed parallel to the HMD display
  • Sample marker placement: Top view.
  • Sample marker placement: Side view. The two side markers are aligned along the eye-level of the user.

HMD Rigid Body in Motive

The two landmark markers closely aligned to the x-axis of the global axes. When the rigid body is created, the orientation of the rigid body itself closely aligns with the global coordinate system.

Creating HMD Rigid Body

For HMD tracking, a modified rigid body needs to be defined in Motive. One important note here is that the rigid body orientation must closely align with the display for the best experience. To accomplish this, it is best to align both the HMD and the rigid body orientation along the global axes. This will ensure an appropriate orientation of the HMD rigid body to be exported.

  1. Place the HMD upright on the floor
  2. Click Viewport2.png and switch to orthographic top view.
  3. While monitoring the View pane, align the two landmark markers along the global x-axis in Motive.
  4. Select the HMD markers and create a rigid body.

Creating a rigid body this way will roughly align its orientation with the orientation of the physical HMD component as well as the global coordinate axes in Motive. This will make it easier when precisely adjusting the pivot point position and orientation later. To display the rigid body orientation axes, set the Orientation to true in the rigid body display settings.

Rigid Body Settings

Rigid body properties for the HMD asset.

After creating a rigid body for the HMD, select the asset in the project pane, and access the corresponding rigid body properties. Adjust the rigid body properties as the following:


Deflection setting is the tolerable distance, in millimeters, that a rigid body marker may deviate from its expected position before it is unlabeled and unassociated with the rigid body. The deflection is set to 4 mm by default. For HMD tracking applications, we recommended lowering this value to 3 or 2. This will reduce the amount of computation required for labeling, and overall latency may be reduced.

Tracking Algorithm

Use the level 3 tracking algorithm (or ray-based tracking). The tracking algorithm setting determines which protocol to use for solving the rigid body in Motive. This algorithm is recommended because it is less susceptible to marker occlusions and solves rigid bodies more robustly without introducing trajectory gaps. This is more suitable for tracking the HMD since even minor occlusions can acutely affect the experience.

User Data

The User Data value for each rigid body is used as an identification number to reference the rigid body in external applications. Log this value for each rigid body (including the HMD(s)) in the scene. This number will be used to associate the assets in UE4 using the plugin devices.

Min Marker Count

The minimum marker count required for the rigid body solve is set to 3 by default. To prevent the swapping of the rigid body definition, you may want to increase this value to 4. When tracking multiple HMDs, there could be limitations to a variety of unique marker arrangements that could be achieved. If this value is set to 3, a set of three markers on an HMD may be congruent to another set in a different HMD, and the rigid body definitions may be switched in Motive.

Rigid Body Pivot Point

As mentioned previously, the position and orientation of the HMD rigid body pivot point need to be carefully adjusted. This section provides recommended methods and steps to accomplish this. When adjusting the pivot point, the following criteria must be achieved:

  • The pivot point is placed on the bridge of the nose; specifically, right at the midpoint between two eyes.
  • Orientation axes of the rigid body should precisely align with the physical HMD component.

Pivot Point Position

For best virtual experiences, the pivot point of the HMD rigid body, in Motive, needs to be positioned on the midpoint between two eyes, of the user when the HMD is put on. To locate this, use the side and top-center landmark markers as references. For more information on adjusting rigid body pivot points, please read through the Rigid Body Tracking page.

1. Set the pivot point over the landmark marker. Use the Set Pivot Point to Selected Marker feature to assign the pivot point to the marker. This will set the elevation of the pivot point along the eye-level.

  • Top view: Rigid body pivot point is assigned to the left landmark marker.
  • Side view: Now both the landmark marker and the pivot point is positioned along the user's eye-level elevation.

2. Place the pivot point at the midpoint between the two markers. Enable Two Marker Distance visual aid Viewport16.png from the perspective pane, and select the two landmark markers in Motive. This will provide a distance between two markers. Then, using this information, translate the pivot point laterally by half of the distance so that it is placed right on the midpoint between two markers.

Translating the pivot point by half of the measured distance to place it at the midpoint.

3. Translate the pivot point along the z-axis using the translation tool. For the most accurate position, you may need to physically measure the sagittal, z-axis, distance from the landmark marker to the root of nose, and apply the measured offset.

  • Pivot point translated along the z-axis
  • Perspective view of the adjusted pivot point position.


Now that you have translated the pivot point, you need to make detailed adjustments to the orientation using the orientation transformation tool. For best results, align the two front markers along the x-axis grid and roughly center the rigid body along the z-axis grid. Then, check to make sure that each of the rigid body orientation axes is parallel to the grids lines in Motive. If there is any deviation, apply rotation to adjust the offset. If needed, transparency of the axes and the grids can be adjusted from the Application settings.

  • In Unreal Engine: the X-axis of the HMD rigid body must be directed forward.
  • In Unity: the Z-axis of the HMD rigid body must be directed forward.
  • Slight offset in the rigid body orientation.
  • After Adjusting, the rigid body orientation axes are precisely aligned with the global axes of Motive

Tip: Once you have the rigid body asset for the HMD configured, you can export the asset into a TRA file for future uses. Importing the TRA file (e.g. CV1.tra) will load the rigid body (HMD) asset and make it available for use; however, the marker placement must remain unchanged in order to re-load previously created rigid bodies.