How to access the HoloLens2 Origin SpatialCoordinateSystem-CodePudding

The problem: I've been working on trying to create a 3D position in Worldspace based on a 2D face RGB face detection, similar to this Microsoft example. I am using Unity 2020.3.16f1, MRTK 2.8.2 and C# for the Unity scripts. I have been able to convert the C code shown in the link to C# with a lot of success. One final issue is accessing the HoloLens 2 origin SpatialCoordinateSystem to be used in the Transform between the camera's 2D coordinate system and the 3D worldspace system.

The SO question at this link asks a very similar question, and I have tried to use SpatialLocator.GetDefault().CreateStationaryFrameOfReferenceAtCurrentLocation().CoordinateSystem() as the answers suggest. I call this function in Unity's "Awake" method, to ensure it is set as early as possible, as shown below.

    private void Awake()
{
   worldSpatialCoordinateSystem = SpatialLocator.GetDefault().CreateStationaryFrameOfReferenceAtCurrentLocation().CoordinateSystem;
}

Problem is that, if the user's headset is moving while the application starts, I notice an offset in the 3D locations commensurate with the direction/position of the head when the application was starting. I have narrowed the problem down to the fact that the HL2 and Unity set an origin SpatialCoordinateSystem just before the function in Awake is called, accounting for the offset between what I expect and what I see.

What I've tried: I have tried using some of the other solutions listed here as well. I cannot use UnityEngine.Windows.WebCam.PhotoCapture becuase of the way I am create still image captures, and (SpatialCoordinateSystem)Marshal.GetObjectForIUnknown(WorldManager.GetNativeISpatialCoordinateSystemPtr()) appears to be deprecated and unusable. Finally, I tried CreateStationaryFrameOfReferenceAtCurrentLocation(Vector3, Quaternion), and used the inverse of the current Camera.main position and rotation, hoping to compensate for the offset, but it did not appear to work (NumericsConversionExtensions is the UnityEngine-to-System.Numerics converver found here). That code is below.

worldSpatialCoordinateSystem = SpatialLocator.GetDefault().CreateStationaryFrameOfReferenceAtCurrentLocation(NumericsConversionExtensions.ToSystem(Camera.main.transform.position*-1), 
        NumericsConversionExtensions.ToSystem(Quaternion.Inverse(Camera.main.transform.rotation))).CoordinateSystem;

My question: Is there either another way to access the origin spatial coordinates or possibly to compensate for the offset when the user is moving their head before Awake is called?

CodePudding user response：

I spent 3 days working on the solution, and found one 1 hour after asking SO. For those who come here, use the code below.

using Microsoft.MixedReality.OpenXR;
worldSpatialCoordinateSystem = PerceptionInterop.GetSceneCoordinateSystem(Pose.identity) as SpatialCoordinateSystem;