Hi @Claude_V,
If I’m understanding your issue correctly, you’re expecting the Height property to mean the height above terrain. In Cesium for Unity, the Height of the CesiumGeoreference refers to the height above the WGS84 ellipsoid model. This is often unequal to the actual height of the terrain above mean sea level.
If you want the height above the terrain, you’ll have to use Physics.Raycast and raycast towards the center of the globe. If you want the height above mean sea level, see Kevin’s post on this thread: The height of the sea is not 0 - #8 by Kevin_Ring