Spatial Anchor with Urho on HoloLens

Does anybody know how to use Spatial Anchors with Urho? I've looked at all the samples, didn't find anything. Nothing in the documentation either. I tried using regular Holographic API:

    var store = await SpatialAnchorManager.RequestStoreAsync();
    var anchors = store.GetAllSavedAnchors();
    store.TrySave("myanchor", SpatialAnchor.TryCreateRelativeTo(???SpatialCoordinateSystem???));

but I don't know where to get the Spatial Coordinate System from.

You can create spatial anchors like this

var anchor = SpatialAnchor.TryCreateRelativeTo(UrhoAppView.Current.ReferenceFrame.CoordinateSystem, new System.Numerics.Vector3(x, y, -z));
store.TrySave("anchorname", anchor);

Note that Urho has a left-handed coordinate system while HoloLens API has a right-handed coordinate system hence the minus z.

You can map an anchor to the current system like this:

    var matrix = store["anchorname"].CoordinateSystem.TryGetTransformTo(UrhoAppView.Current.ReferenceFrame.CoordinateSystem);
    if (matrix.HasValue)
    {
       System.Numerics.Vector3 scale;
       System.Numerics.Quaternion rotation;
       System.Numerics.Vector3 translation;

       System.Numerics.Matrix4x4.Decompose(matrix.Value, out scale, out rotation, out translation);

       var q = new Quaternion(rotation.X, rotation.Y, rotation.Z, rotation.W);

       var v = new Vector3(translation.X, translation.Y, -translation.Z);// -Z Right-handed to left-handed
    }