C Specification

xrLocateSpace provides the physical location of a space in a base space at a specified time, if currently known by the runtime.

XrResult xrLocateSpace(
    XrSpace                                     space,
    XrSpace                                     baseSpace,
    XrTime                                      time,
    XrSpaceLocation*                            location);

Parameters

Parameter Descriptions
  • space identifies the target space to locate.

  • baseSpace identifies the underlying space in which to locate space.

  • time is the time for which the location should be provided.

  • location provides the location of space in baseSpace.

Description

For a time in the past, the runtime should locate the spaces based on the runtime’s most accurate current understanding of how the world was at that historical time.

For a time in the future, the runtime should locate the spaces based on the runtime’s most up-to-date prediction of how the world will be at that future time.

The minimum valid range of values for time are described in https://www.khronos.org/registry/OpenXR/specs/1.0/html/xrspec.html#prediction-time-limits. For values of time outside this range, xrLocateSpace may return a location with no position and XR_SPACE_LOCATION_POSITION_VALID_BIT unset.

Some devices improve their understanding of the world as the device is used. The location returned by xrLocateSpace for a given space, baseSpace and time may change over time, even for spaces that track static objects, as one or both spaces adjust their origins.

During tracking loss of space relative to baseSpace, runtimes should continue to provide inferred or last-known position and orientation values. These inferred poses can, for example, be based on neck model updates, inertial dead reckoning, or a last-known position, so long as it is still reasonable for the application to use that pose. While a runtime is providing position data, it must continue to set XR_SPACE_LOCATION_POSITION_VALID_BIT but it can clear XR_SPACE_LOCATION_POSITION_TRACKED_BIT to indicate that the position is inferred or last-known in this way.

If the runtime has not yet observed even a last-known pose for how to locate space in baseSpace (e.g. one space is an action space bound to a motion controller that has not yet been detected, or the two spaces are in disconnected fragments of the runtime’s tracked volume), the runtime should return a location with no position and XR_SPACE_LOCATION_POSITION_VALID_BIT unset.

The runtime must return a location with both XR_SPACE_LOCATION_POSITION_VALID_BIT and XR_SPACE_LOCATION_POSITION_TRACKED_BIT set when locating space and baseSpace if both spaces were created relative to the same entity (e.g. two action spaces for the same action), even if the entity is currently untracked. The location in this case is the difference in the two spaces' application-specified transforms relative to that common entity.

The runtime should return a location with XR_SPACE_LOCATION_POSITION_VALID_BIT set and XR_SPACE_LOCATION_POSITION_TRACKED_BIT unset for spaces tracking two static entities in the world when their relative pose is known to the runtime. This enables applications to make use of the runtime’s latest knowledge of the world, even during tracking loss.

If an XrSpaceVelocity structure is chained to the next pointer of XrSpaceLocation and the velocity is observed or can be calculated by the runtime, the runtime must fill in the linear velocity of the origin of space within the reference frame of baseSpace and set the XR_SPACE_VELOCITY_LINEAR_VALID_BIT. Similarly, if an XrSpaceVelocity structure is chained to the next pointer of XrSpaceLocation and the angular velocity is observed or can be calculated by the runtime, the runtime must fill in the angular velocity of the origin of space within the reference frame of baseSpace and set the XR_SPACE_VELOCITY_ANGULAR_VALID_BIT.

The following example code shows how an application can get both the location and velocity of a space within a base space using the xrLocateSpace function by chaining an XrSpaceVelocity to the next pointer of XrSpaceLocation and calling xrLocateSpace.

XrSpace space;      // previously initialized
XrSpace baseSpace;  // previously initialized
XrTime time;        // previously initialized

XrSpaceVelocity velocity {XR_TYPE_SPACE_VELOCITY};
XrSpaceLocation location {XR_TYPE_SPACE_LOCATION, &velocity};
xrLocateSpace(space, baseSpace, time, &location);
Valid Usage (Implicit)
  • space must be a valid XrSpace handle

  • baseSpace must be a valid XrSpace handle

  • location must be a pointer to an XrSpaceLocation structure

  • Both of baseSpace and space must have been created, allocated, or retrieved from the same XrSession

Return Codes
On success, this command returns
  • XR_SUCCESS

  • XR_SESSION_LOSS_PENDING

On failure, this command returns
  • XR_ERROR_VALIDATION_FAILURE

  • XR_ERROR_RUNTIME_FAILURE

  • XR_ERROR_HANDLE_INVALID

  • XR_ERROR_INSTANCE_LOST

  • XR_ERROR_SESSION_LOST

  • XR_ERROR_TIME_INVALID

See Also

Document Notes

For more information, see the OpenXR Specification

This page is extracted from the OpenXR Specification. Fixes and changes should be made to the Specification, not directly.

Copyright (c) 2014-2021, The Khronos Group Inc.