Class ARSessionOrigin

An ARSessionOrigin is the parent for an AR setup. It contains a Camera and any GameObjects created from detected features, such as planes or point clouds.

Inheritance
Object
Object
Component
Behaviour
MonoBehaviour
ARSessionOrigin
Inherited Members
Namespace: UnityEngine.XR.ARFoundation
Syntax
[DisallowMultipleComponent]
[HelpURL("https://docs.unity3d.com/Packages/com.unity.xr.arfoundation@4.1/api/UnityEngine.XR.ARFoundation.ARSessionOrigin.html")]
public class ARSessionOrigin : MonoBehaviour
Remarks

Session space vs Unity space

Since an AR device will be used to drive the Camera's position and rotation, you cannot directly place the Camera at an arbitrary position in the Unity scene. Instead, you should position the ARSessionOrigin. This will make the Camera (and any detected features) relative to that as a result.

It is important to keep the Camera and detected features in the same space relative to each other (otherwise, detected features like planes won't appear in the correct place relative to the Camera). We call the space relative to the AR device's starting position "session space" or "device space". For example, when the AR session begins, the device may report its position as (0, 0, 0). Detected features, such as planes, will be reported relative to this starting position. The purpose of the ARSessionOrigin is to convert the session space to Unity world space.

To facilitate this, the ARSessionOrigin creates a new GameObject called "Trackables" as a sibling of its Camera. This should be the parent GameObject for all detected features.

At runtime, a typical scene graph might look like this:

  • AR Session Origin
  • Camera
  • Trackables
    • Detected plane 1
    • Detected plane 2
    • Point cloud
    • etc...

You can access the "trackables" GameObject with trackablesParent.

Note that the localPosition and localRotation of detected trackables remain in real-world meters relative to the AR device's starting position and rotation.

Scale

If you want to scale the content rendered by the ARSessionOrigin you should apply the scale to the ARSessionOrigin's transform. This is preferrable to scaling the content directly as that can have undesirable side-effects. Physics and NavMeshes, for example, do not perform well when scaled very small.

Properties

camera

The Camera to associate with the AR device. It must be a child of this ARSessionOrigin.

Declaration
public Camera camera { get; set; }
Property Value
Type Description
Camera
Remarks

The Camera should update its position and rotation according to the AR device. This is typically accomplished by adding a TrackedPoseDriver component to the Camera.

trackablesParent

The parent Transform for all "trackables", e.g., planes and feature points.

Declaration
public Transform trackablesParent { get; }
Property Value
Type Description
Transform

Methods

MakeContentAppearAt(Transform, Quaternion)

Makes content appear to have orientation rotation relative to the Camera.

Declaration
public void MakeContentAppearAt(Transform content, Quaternion rotation)
Parameters
Type Name Description
Transform content

The Transform of the content you wish to affect.
Quaternion rotation

The rotation the content should appear to be in, relative to the Camera.
Remarks

This method does not actually change the Transform of content; instead, it updates the ARSessionOrigin's Transform such that it appears the content is in the requested orientation.

MakeContentAppearAt(Transform, Vector3)

Makes content appear to be placed at position.

Declaration
public void MakeContentAppearAt(Transform content, Vector3 position)
Parameters
Type Name Description
Transform content

The Transform of the content you wish to affect.
Vector3 position

The position you wish the content to appear at. This could be a position on a detected plane, for example.
Remarks

This method does not actually change the Transform of content; instead, it updates the ARSessionOrigin's Transform such that it appears the content is now at the given position.

MakeContentAppearAt(Transform, Vector3, Quaternion)

Makes content appear to be placed at position with orientation rotation.

Declaration
public void MakeContentAppearAt(Transform content, Vector3 position, Quaternion rotation)
Parameters
Type Name Description
Transform content

The Transform of the content you wish to affect.
Vector3 position

The position you wish the content to appear at. This could be a position on a detected plane, for example.
Quaternion rotation

The rotation the content should appear to be in, relative to the Camera.
Remarks

This method does not actually change the Transform of content; instead, it updates the ARSessionOrigin's Transform such that it appears the content is now at the given position and rotation. This is useful for placing AR content onto surfaces when the content itself cannot be moved at runtime. For example, if your content includes terrain or a nav mesh, then it cannot be moved or rotated dynamically.

Events

trackablesParentTransformChanged

Invoked during Application.onBeforeRender whenever the trackablesParent transform changes.

Declaration
public event Action<ARTrackablesParentTransformChangedEventArgs> trackablesParentTransformChanged
Event Type
Type Description
Action<ARTrackablesParentTransformChangedEventArgs>