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 EventTargetXRReferenceSpace 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  EventTargetXRReferenceSpace 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 reference space returned by XRSession.requestReferenceSpace() is either XRReferenceSpace or XRBoundedReferenceSpace. The "Interface" column in the table below indicates which of the two types is returned for each reference space type constant.

XRReferenceSpaceType Description Interface
bounded-floor 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. XRBoundedReferenceSpace
local

A 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.

XRReferenceSpace
local-floor 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 thet 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). XRReferenceSpace
unbounded A 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 accomodate that need. XRReferenceSpace
viewer A 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. XRReferenceSpace

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 Status Comment
WebXR Device API
The definition of 'XRReferenceSpace' in that specification.
Working Draft Initial definition.

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
XRReferenceSpaceChrome Full support 79Edge No support NoFirefox No support NoIE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android Full support 79Firefox Android No support NoOpera Android No support NoSafari iOS No support NoSamsung Internet Android No support No
getOffsetReferenceSpace()Chrome Full support 79Edge No support NoFirefox No support NoIE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android Full support 79Firefox Android No support NoOpera Android No support NoSafari iOS No support NoSamsung Internet Android No support No
onresetChrome Full support 79Edge No support NoFirefox No support NoIE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android Full support 79Firefox Android No support NoOpera Android No support NoSafari iOS No support NoSamsung Internet Android No support No
reset eventChrome Full support 79Edge No support NoFirefox No support NoIE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android Full support 79Firefox Android No support NoOpera Android No support NoSafari iOS No support NoSamsung Internet Android No support No

Legend

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See also