APS Live Link

Tracked Props

Download The Model!

Download the baseball bat model from Blendswap.com:

Note, Blender is optional, most 3D manipulation software should be able to export as .fbx and works equally well.

In the next part we will simply download the model and open it in Blender, from there we can export a new .fbx to use for the game model. First before exporting the .fbx we will need to clear any rotation and clear any scale so the model's scale is 1:1 and centered on the origin.

Open The .blend Model

Open the baseball bat model using Blender. You should see the mesh of the baseball bat in the viewport:

blender to fbx.mp4

Video shows loading a .blend model in Blender and clearing the rotation and location attributes, then adjusting the scale to a value so the model's dimensions match the real-world physical object. Then exported as a .fbx with export option.

📝Important. The model is not at the origin and is rotated slightly off axis. For perfect alignment it is critical that the rotation and location and scale must all be cleared, and applied before exporting the .fbx so the exported model is guaranteed to be located at the origin and the model's scale will be 1:1 in all applications.

📝Important. For this tutorial the bat model was arbitrarily scaled to exactly 1 meter. If you have a physical prop (eg. toolbox with tracker attached) make sure to scale the toolbox model to be the exact same dimensions (in meters) as the real/physical item.

If the tracker was attached to a real baseball bat then I could measure the exact dimensions, eg. If the IRL bat and live link bat model are identical dimension and tracker alignment is precise the motion capture would appear realistic with mass and inertia and real collisions !

🍎Properly aligned tracker/model won't clip through the floor when set down or dropped!

Blank Unity Project

A blank Unity 2019.4 project with the APS_SDK imported to build the mocap prop asset:

Unity prop.mp4

A video of the Unity editor with a newly created project and the APS_SDK imported to build a prop with a fixed tracker offset target.

📝Important. Unity editor 2019.4.40f1 is the recommended version to use when building mocap assets for Mocap Fusion.

📝Important. After the Unity project loads make sure you have imported the latest APS_SDK by dragging and dropping the APS_SDK.unitypackage to the viewport.

Download the latest APS_SDK from the APS Discord or the Props Tutorial and import it into the Unity project.

In the APS_SDK look for the TrackerPointTarget prefab you can add to props to specify a fixed tracker offsets so the prop will snap to the fixed offset whenever attached to a tracker.

Tracker Serial

📝Important. The end of the video shows the Tracker Serial number field. This is needed so the prop will automatically attach to the correct tracker and will always use that tracker.

Assign the Tracker Serial of the tracker attached to the physical prop. Check APS trackers setup panel to find the properly formatted serial name of the tracker, copy that value exactly and include all characters and capitalization.

Copy Asset

After rebuilding the prop a new folder should appear, copy the prop$baseball-bat prop to the VR_MocapAssets folder

Mocap Prop Complete

The mocap prop should now be available in the game. Before we can use it with live-link we also need to add the .fbx to a UE live link Blueprint.

UE Prop Blueprint

Adding the .fbx to a new UE project that includes the APS Live Motion Capture live-link plugin. The basic idea is to find the existing TrackerObject Blueprint and create a duplicate, then delete the cube mesh and add the mesh from the .fbx ensuring the model is placed at the origin:

UE prop.mp4

After adding the .fbx to the UE project and importing the file, create a duplicate of the TrackerObject blueprint and edit it to delete the cube mesh and repace it with the custom baseball bat mesh. Then by setting the Tracker ID to a coorisponding Vive tracker the object will sync with that tracke when live-link is activated.

Download the APS Live Link plugin from the FAB.

The Live-Link Plugin Setup Tutorial

📝Important. In the latest APS update Virtual Trackers has slightly changed. Now whenever a tracker is connected to a VR prop the live-link server sends the prop's origin coordinates instead of the tracker's origin. This makes it intuitive when creating the prop Blueprints as there is no need to offset the model or worry about pivot points, simply add the model at the Blueprint's origin.

📝Important. For virtual trackers to function you must assign the correct Tracker ID for the Blueprint and is shown in the video. These are the nodes responsible for live-link location:

Look for the TrackerObject Blueprint included with the APS live-link plugin. This allows syncing with the Vive trackers in APS and includes a simple node setup in the Event graph. Or duplicate the TrackerObject blueprint and use it with a custom model!

UE Blueprint Complete

The fbx is now imported into the UE project and has been added to a tracked blueprint. The Blueprint has been added to the scene with the APSCore and is ready for live link!

Connect Live-Link

To check if live-link works first launch the VR game from Steam, then press play in the UE editor. If the virtual trackers are configured correctly you should see the TrackerObject in the UE scene start moving with tracker in VR.

Note immediately after the prop is added in VR the location of the TrackerObject in UE snaps the new prop pivot location, and how the bat model in UE then instantly aligns with the prop in VR:

bat prop live link.mp4

A video of the animated virtual trackers and live-link prop with both applications connected and a side by side view of the tracked prop in both windows.

📝Important. Make sure the firewall settings are not blocking either UnrealEditor or MocapFusion.

📝Important. Ensure that "Run In Background" is enabled in both applications so both windows will run at full framerate.

If the TrackerObject is configured it should track with the Vive tracker in VR, but also note that when adding the bat prop in VR it automatically linked to the tracker immediately after being added, this is because we assigned a serial number which matched the tracker - without any need for user alignment - and makes it simple to add tracked props ready for mocap instantly!

Take special note of how the TrackerObject in UE location changed to the prop pivot the instant the bat prop was added in VR, because the prop we built earlier includes a TrackerPointTarget - live-link detects this component and then sends the prop's origin rather than the tracker's origin.

Making it simple to create Blueprints for props.

Conclusion

I hope you found this tutorial helpful.

And I hope you enjoy using the live link plugin!

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