Hololens2 Correct Usage of SpatialAnchors - hololens

Question

I am trying to implement an Hololens 2 App using SpatialAnchors but it seems that I am not quite understanding the concept right. I am able to create, save and restore SpatialAnchors of the Windows.Perception.Spatial namespace, but whenever I restore them they are placed relative to the start position of the headset.
I use this snippet to create an anchor:
SpatialAnchor thisAnchor = SpatialAnchor.TryCreateRelativeTo(coord);
And this to get the relative SpatialCoordinateSystem (from this post)
public static bool UseSGIPSceneCoordinateSystem(out SpatialCoordinateSystem sGIPSceneCoordinateSystem)
{
// gain access to the scene object
SceneObserverAccessStatus accessStatus = Task.Run(RequestAccess).GetAwaiter().GetResult();
if (accessStatus == SceneObserverAccessStatus.Allowed)
{
Scene scene = Task.Run(GetSceneAsync).GetAwaiter().GetResult();
sGIPSceneCoordinateSystem = SpatialGraphInteropPreview.CreateCoordinateSystemForNode(scene.OriginSpatialGraphNodeId);
return true;
}
else
{
sGIPSceneCoordinateSystem = null;
return false;
}
}
I use this method to restore the SpatialAnchor I need:
public bool GetAnchor(string id, out SpatialAnchor anchor)
{
[...]
_anchors = _anchorStore.GetAllSavedAnchors();
foreach (var kvp in _anchors)
{
if(kvp.Key == id)
{
anchor = kvp.Value;
return true;
}
}
anchor = null;
return false;
}
And this to process the restored Anchor and get a place in the scene for it:
public void SomeOtherMethod(SpatialAnchor anchor)
{
SpatialCoordinateSystem showcaseCoordinateSystem = anchor.CoordinateSystem;
//get the reference SpatialCoordinateSystem
if (!UseSGIPSceneCoordinateSystem(out SpatialCoordinateSystem referenceCoordinateSystem))
return;
_anchorMatrix = showcaseCoordinateSystem.TryGetTransformTo(referenceCoordinateSystem);
System.Numerics.Matrix4x4 _notNullMatrix = _anchorMatrix.Value;
Matrix4x4 unityAnchorMatrix = _notNullMatrix.ToUnity();
anchorGameObject.transform.FromMatrix(unityAnchorMatrix);
}
I think that I am using the wrong SpatialCoordinateSystem but can´t find information on how to get a SpatialCoordinateSystem which the HoloLens2 generates for the physical spatial surrounding of the user that is persistent.
I am using:
Unity 2020.3.13f1
OpenXR Plugin 1.3.1
MRTK 2.7.3
MRTK-OpenXR 1.2.1
MRTK SceneUnderstanding 0.6.0
I am also confused of the amount of different SpatialAnchor-Systems, reference coordinatesystems and the documentation. Every post I find about SpatialAnchors seems to use a different approach. There seems to be SpatialAnchor-Systems for the Unity WLT, UnityEngine.VR.WSA with WorldManager, Azure Spatial Anchors,
UnityEngine.XR.WindowsMR.WindowsMREnvironment, etc.
And unless I havent overseen it, the microsoft documentation is not really clear about which one to use and how to use it right.
I would be really thankful if someone could bring some light into this issue.
I posted this question also on forum.unity.com