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.
Inherited Members
Namespace: UnityEngine.XR.ARFoundation
Syntax
[DisallowMultipleComponent]
[HelpURL("https://docs.unity3d.com/Packages/com.unity.xr.arfoundation@3.0/api/UnityEngine.XR.ARFoundation.ARSessionOrigin.html")]
public class ARSessionOrigin : MonoBehaviourRemarks
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 |
| Quaternion | rotation | The rotation the content should appear to be in, relative
to the |
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 |
| 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 |
| 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 |
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.