Unreal Engine: Skeleton Streaming

Main Page → Motive Documentation → OptiTrack Unreal Engine 4 Plugin → Unreal Engine Skeleton Streaming

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Page Scope

This page provides instructions on how to set up skeleton streaming using the Unreal Engine plugin. Please note that this feature is supported for plugin version 4.19 or above only.

Skeleton Bone Mapping

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Skeleton streaming is supported only in plugin versions 1.9 or above.

Tutorial Video

For UE plugin versions higher than 2.0.3 For plugin versions above 2.0.3, the plugin folder must be placed within the UE project directory. Each project in UE is created and stored in a project folder. In this directory, copy and paste the OptiTrack folder extracted from the ZIP file into the Plugins folder. If the folder doesn't exist already, you may need to create a new folder and name it Plugins. After the set up, you will have the OptiTrack plugin included in your project: [Project Folder]\Plugins\Optitrack .

Setup

Follow the below steps to set up skeleton streaming onto Unreal Engine.

1. Create a Animation Blueprint in the 3D View

Step 1. Navigate to a character folder. With Paragon sample characters, it is located in Characters → Heros → [Character Name] → Meshes.

Step 2. Right-click the blank space in the Content Browser pane, then select Animation → Animation Blueprint.

Step 3. On the pop-up window, select the OptiTrackAnimInstance at the parent class section at the top and click on the target skeleton name at the bottom. Then click OK.

Step 4. AIn the content browser, assign a name to the created animation blueprint.

Step 4. Drag the character blueprint into the scene.

Step 5. Select the character blueprint in the 3D View

• In the Details Pane, select “+ Add Component” and create a new an “OptiTrack Skeleton Component” on the model.
• Set the “Source Skeleton Asset” equal to the skeleton name in Motive.

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  Adding animation blueprint in UE.
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  Specifying skeleton name under OptiTrack Skeleton Component properties.
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  Creating animation blueprint.

2. Setup the Blueprint

Step 1.Double-click the animation blueprint in the content browser to open its editor.

Step 2.Right-click the animation graph, then create a new "OptiTrack Skeleton".

Step 3.Right-click the animation graph, then create a new "Get Streaming Client Origin" and connect its output to the Streaming Client Origin.

Step 4.Right click the animation graph, then create a new "Get Source Skeleton Asset Name" and connect its output to the Source Skeleton Asset Name.

Step 5.Connect all of the nodes together. Specifically, drag the person icon in the "OptiTrack Skeleton" to the person icon on the "Final Animation Pose".

Roll Bone Interpolation For characters with shoulder roll bones, the skeleton plugin will detect its existence and apply a slight twist to the roll bone to keep the swinging motion of the arms is smooth. In the OptiTrack Skeleton blueprint, you can enable/disable this feature using the Roll Bone Interpolation checkbox, and you can also change how much of twist is applied by adjusting the Roll Bone Blending parameter. When this parameter is set to 0, plugin will not affect roll bone motion at all, and when this is set to 1, the plugin will attempt to fix the roll bone with no twist at all. Please note that this feature may not work on some characters.

3. Assign Bone Mapping

Step 1. Select the OptiTrack Skeleton plugin in the blueprint graph area.

Step 2. Drop down the Bone Mappings property in the Details Pane.

Step 3. Click “Auto Fill Bone Mapping” to automatically assign the bones in the skeleton to the OptiTrack skeleton names.

Note: There is no standard for bone naming conventions, so bone names may vary depending on characters. After doing the auto-fill, review the list and double-check that the auto-assigned names are correct. You may need to manually use the drop-down menu to adjust the assigned mapping for missing, or incorrect, items.

Step 4. Hit "Compile" in the top left to build the blueprint.

Auto-mapped skeleton bones.

4. Setup OptiTrack Streaming

Step 1. Open the 3D View

Step 2. Search OptiTrack Client Origin in the Modes pane.

Step 3. Drag the OptiTrack Client Origin into the 3D scene, then select it to access its properties.

• (Optional) put it at 0,0,0 location.
• Make sure that streaming settings on both Motive and Unreal match.

See: OptiTrack Unreal Engine page for more instructions on setting up the client origin.

5. Click Play

Notes on bone mapping

The OptiTrack Unreal Engine Skeleton Plugin uses bone mapping, not retargeting. This means that the bone segments in Motive map directly to the character model (bone mapping), instead of being translated into something that is usable by a more abstract biped model (retargeting). Because of this non-anatomical skeletons will not map correctly without some additional tweaking.

Practically, this means that you will need to do things like turn off the toe mapping for characters with high heels, adjusting the pelvis bone in Motive or in the model for characters with non-anatomical hip bones, and not use bipeds that are too anatomically different than humans, such as a gorilla or swamp monster.

For example, the character sample below has both a non-anatomical pelvis and high heels. It is preferable to use character models that are more anatomically correct, but in this case, you can do a couple things to mitigate these issues:

1. Turn-off toe streaming

In the example below, since this character is wearing heels, any actor providing data for this model will also need to be wearing heels. To get around this you can just turn off the toe mapping in the OptiTrack Unreal Engine Skeleton Plugin.

2, Adjust the bone segments in Motive

The hip segment on the Countess actor is centered in the stomach rather than in the pelvis, the neck bone in Motive is a bit too long for the model, and the shoulders in Motive do not match the width of the character’s shoulders. By adjusting bones' positions and lengths in Motive, you can make the streamed skeleton to better match the model; however, please note that there are limitations to how much you can do this.)

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