Coordinate question about Cesium and Babylon

When i promote my project about Cesium with Babylon,hanppened to two problems.
First,I import a .gltf model in Babylon`s canvas but if I move the camera,the model maybe the scene begins jitter,which is the reason that Babylon synchronize the coordinate in Cesium.
Secondly,i try to add a billboard in a point in model,but the billboard appear out of the earth of Cesium,I think maybe the coordinate question about Cesium and Babylon.
So may someone can set up a planto resolve this question,a code in github will be better

Maybe that can help:

Also, regarding the jittering, you can try using the useHighPrecisionMatrix: true option when creating the engine. See for eg: