# Outside-in (Optitrack/Vicon) Setup

When combined with a powerful optical, outside-in motion tracking hardware such as [Optitrack](https://optitrack.com/) or [Vicon, ](https://www.vicon.com/)Existent can help you create applications in large physical spaces, with effectively unlimited numbers of tracked props and a high degree of accuracy.

This setup combines the head position from HMDs with body and object tracking provided by the outside in motion capture system. The key to getting this all to work well together is aligning the origin of the outside-in system with the origin of the HMD - this is done using Existent’s [alignment tooling](https://docs.existent.com/documentation/learning-existent/getting-started/adding-tracked-objects/outside-in-optitrack-vicon-setup/aligning-hmds-with-outside-in-systems). 

In this configuration, you should think of the origin of the outside-in system as the authoritative origin with headset origins being adjusted to match it.

Optitrack, Vicon and the majority of other outside-in systems have livelink integrations via plugins that can be downloaded from their respective websites. Existent works with these systems via LiveLink. 

To setup LiveLink:

1. Download the correct LiveLink Plugin from the providers' websites: [Optitrack](https://optitrack.com/support/downloads/plugins.html#unreal-plugin), [Vicon](https://www.vicon.com/software/third-party/unreal-engine/)
2. Install the plugin into your project using the instructions provided by the plugin vendor.
3. Open Unreal Engine and ensure the LiveLink Plugin and the plugin you just installed are enabled.
4. Open the LiveLink window.<br>

   <figure><img src="https://lh7-us.googleusercontent.com/zLlSBKPRgWnm1RuNxibhti-ysSIyUdfH8r87vkVBx-ofpVl8BfwkAn3zV77Hya1TQ8fqYickedG_L0GZRDWa3JWKSvxQEz4VqYeXr82kFVzbpxXfHgrkvYNDxfbybqrO5fe2Sdu881qKtY-3rLys3A" alt=""><figcaption></figcaption></figure>
5. Add a new LiveLink source. If your machine is connected to your mocap system it should show all of the tracked items.<br>

   <figure><img src="https://lh7-us.googleusercontent.com/gkHN_dRKd2pkVKJwDHAcP1sc_Qohf5N84nue_rzq1OnE7MSYWMyVgMbpvzIjll_kwaKMD_lMib--o5sFiNnkM5I8yyjxFFHmsSskRI9fM-3HftdA5Nth6-LbZxmoTiIRD4Hl4Btc9vbriU5XrY15TA" alt=""><figcaption></figcaption></figure>
6. Create a LiveLink preset.
7. In project settings set the Default LiveLink preset to the preset you just created and then set Existent’s default tracking system to LiveLinkTrackingSystem.

   <figure><img src="https://lh7-us.googleusercontent.com/G4PT8yIGgTMI4hULGYAGDELCOXmTBG7meEIUGiITvY2F_kxDGaflxbTydRo2qDPsN1cxeSHfmlp4HXJ6rE9bbaI6BJ-7YpGWvgvVHREdd4f8P0uXS0nJzVTOI_LU54l4YayvtkG7AWITx4T0HN4gVQ" alt=""><figcaption></figcaption></figure>

{% hint style="warning" %}
If you can't see a tracked object working properly and the circle next to the source is orange, double check that the unique ID assigned to it is correct on Optitrack's Motive.
{% endhint %}

{% hint style="warning" %}
When creating a [Stage](https://docs.existent.com/documentation/resources/classes-components/existentstage) ensure that you set the origin of your mocap volume up to be in the exact centre of your Stage. E.g. If your mocap volume is 4x6m then set the origin 2m from one edge and 3m from the other.
{% endhint %}


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