b3dm does not show when defining vertices in ECEF


I am trying to display a b3dm model at a particular position on the globe. I can get it to work if I use a local 0-centered coordinate system for the model and then transform it to the correct position using the transformation matrix in tileset.json.
However, when I position the model geographically (using ECEF coordinates) in the b3dm file, the model doesn't show. When using this approach, I use an identity matrix as transformation matrix and use ECEF coordinates to define the bounding sphere (which does show up at the right location).

As I would prefer to use the latter way of working, any assistance would be very much appreciated.

Both approaches are available here:

Just to add:
I am using the following workflow:
Python shapely polygons are exported using wkb (well known binary). Afterwards I use py3dtiles (https://github.com/Oslandia/py3dtiles) to convert to b3dm. I have the impression that I am losing accuracy somewhere, which might lead to the model ending up inside the globe. I will further investigate and update.


ECEF coordinates should work and should render at the right location, however once you get it working you’ll notice jittering problems which are caused by lack of precision on the GPU. Ultimately the former approach is better.

For reference, we have a sample tileset whose positions are in ECEF coordinates: https://github.com/AnalyticalGraphicsInc/cesium/tree/master/Specs/Data/Cesium3DTiles/Batched/BatchedWGS84