XRReferenceSpace

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The WebXR Device API's XRReferenceSpace interface describes the coordinate system for a specific tracked entity or object within the virtual world using a specified tracking behavior. The tracking behavior is defined by the selected reference space type. It expands upon the base class, XRSpace, by adding support for several different tracking behaviors as well as to request a new reference space which describes the offset transform between the tracked object and another location in the world.

All reference spaces—with the sole exception being bounded reference spaces—are described using the XRReferenceSpace type. Bounded spaces are implemented as XRBoundedReferenceSpace objects. These are special spaces which let you establish a perimeter within which it's "safe" for the viewer to move. For XR systems that allow the user to physically move around, such as those that track movement with a real-world camera, this boundary establishes the edges of the area the user is able to move around in, whether due to physical obstacles or due to limitations of the XR hardware. See the article Using bounded reference spaces to protect the viewer for more on using boundaries to keep the user from colliding with obstacles both physical and virtual.

Properties

In addition to the properties inherited from XRSpace (of which there are none at this time), XRReferenceSpace also inherits the properties of EventTarget. XRReferenceSpace defines no additional properties.

Methods

In addition to the methods inherited from its parent interface, XRSpace (there are none at this time), XRReferenceSpace inherits methods from EventTarget. XRReferenceSpace also provides the following methods.

getOffsetReferenceSpace(): Creates and returns a new reference space object as the same type as the one on which you call the method (so, either XRReferenceSpace or XRBoundedReferenceSpace). The new reference space can be used to transform a coordinate from the reference space of the object on which the method is called into a different coordinate space. This is useful for positioning objects while rendering, and to perform the needed transforms when changing the viewer's position and/or orientation in 3D space.

Events

In addition to other events that may be sent to XRSpace or EventTarget objects, the following also apply to XRReferenceSpace objects.

reset

The reset event is sent to an XRReferenceSpace object when the browser detects a discontinuity has occurred wherein the tracked object's origin relative to the user's environment or location. This can happen, for example, after the user recalibrates their XR device, or if the device automatically adjusts its origin after losing and regaining tracking.

In addition to using addEventListener(), you can establish a reset event handler by setting the onreset event handler property.

Reference space types

The types of reference space are listed in the table below, with brief information about their use cases and which interface is used to implement them.

bounded-floor: An XRBoundedReferenceSpace similar to the local type, except the user is not expected to move outside a predetermined boundary, given by the boundsGeometry in the returned object.
local: An XRReferenceSpace tracking space whose native origin is located near the viewer's position at the time the session was created. The exact position depends on the underlying platform and implementation. The user isn't expected to move much if at all beyond their starting position, and tracking is optimized for this use case. For devices with six degrees of freedom (6DoF) tracking, the local reference space tries to keep the origin stable relative to the environment.
local-floor: An XRReferenceSpace similar to the local type, except the starting position is placed in a safe location for the viewer to stand, where the value of the y axis is 0 at floor level. If that floor level isn't known, the user agent will estimate the floor level. If the estimated floor level is non-zero, the browser is expected to round it such a way as to avoid fingerprinting (likely to the nearest centimeter).
unbounded: An XRReferenceSpace tracking space which allows the user total freedom of movement, possibly over extremely long distances from their origin point. The viewer isn't tracked at all; tracking is optimized for stability around the user's current position, so the native origin may drift as needed to accommodate that need.
viewer: An XRReferenceSpace tracking space whose native origin tracks the viewer's position and orientation. This is used for environments in which the user can physically move around, and is supported by all instances of XRSession, both immersive and inline, though it's most useful for inline sessions. It's particularly useful when determining the distance between the viewer and an input, or when working with offset spaces. Otherwise, typically, one of the other reference space types will be used more often.

Usage notes

Creating an XRReferenceSpace

There are two situations in which you need to obtain an XRReferenceSpace. The first is when you set up your scene and need to obtain a reference space to represent the user's viewpoint on the world for the duration of the XRSession. To do that, call the XRSession method requestReferenceSpace(), specifying the reference space type you wish to obtain.

xrSession.requestReferenceSpace("local").then((refSpace) => {
  xrReferenceSpace = refSpace;
  /* ... */
});

The other situation in which you may need to acquire a new reference space is if you need to move the origin to a new position; this is commonly done, for example, when your project allows the user to move through the environment using input devices such as the keyboard, mouse, touchpad, or game controls that are not connected through the XR device. Since the origin will typically be the user's location in the space, you need to change the origin to reflect their movement and any orientation changes they make.

To move or rotate the user's view of the world, you need to change the XRReferenceSpace used to represent that viewpoint. However, XRReferenceSpace is immutable, so you need to instead create a new reference space representing the changed viewpoint. This is easily done using the getOffsetReferenceSpace() method.

let offsetTransform = new XRRigidTransform({x: 2, y: 0, z: 1},
                                           {x: 0, y: 1, z: 0, w: 1});
xrReferenceSpace = xrReferenceSpace.getOffsetReferenceSpace(offsetTransform);

This replaces the XRReferenceSpace with a new one whose origin and orientation are adjusted to place the new origin at (2, 0, 1) relative to the current origin and rotated given a unit quaternion that orients the space to put the viewer facing straight up relative to the previous world orientation.

Geometry

The native origin of any XRReferenceSpace is always configured so that +X is considered to be to the right, +Y is upward, and +Z is "backward" or toward the user.

Specifications

Specification
WebXR Device API # xrreferencespace-interface

Browser compatibility

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	WebView Android	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet
`XRReferenceSpace`	79	79	No	No	No	No	No	79	No	No	No	11.2
`getOffsetReferenceSpace`	79	79	No	No	No	No	No	79	No	No	No	11.2
`onreset`	79	79	No	No	No	No	No	79	No	No	No	11.2
`reset_event`	79	79	No	No	No	No	No	79	No	No	No	11.2