The read-only XRReferenceSpaceEvent property transform indicates the position and orientation of the affected referenceSpace's native origin after the changes the event represents are applied. The transform is defined using the old coordinate system, which allows it to be used to convert coordinates from the pre-event coordinate system to the post-event coordinate system.

An XRRigidTransform object providing a transform that can be used to convert coordinates from the pre-event coordinate system to the post-event coordinate system.

Upon receiving a reset event, you can apply the transform to cached position or orientation information to shift them into the updated coordinate system. Alternatively, you can just discard any cached positional information and recompute from scratch. The approach you take will depend on your needs.

For details on what causes a reset event and how to respond, see the reset event's documentation.

This example handles the reset event by walking through all the objects in a scene, updating each object's position by multiplying it with the event's given transform. The scene is represented by a scene object, with all the objects in an array called objects within it.

xrReferenceSpace.addEventListener("reset", (event) => {
  for (const obj of scene.objects) {
    mat4.multiply(obj.transform, obj.transform, event.transform);
  }
});