As we known, the UE world coordinate is Cartesian coordinates and Cesium is WGS84, so we need project the WGS84 to a projection coordinates, I want to know the projection params, Is it the Spherical Mercator(EPSG3857)? if it is not, could you tell what is it?
Cesium for Unreal renders a true spherical (actually ellipsoidal) model of the Earth. It doesn’t project the Earth to a plane.
The CesiumGeoreference Actor places the globe such that a given longitude/latitude/height is located at Unreal Engine’s (0,0,0), and such that +Z is “up” at that point. This is a simple translation and rotation, though, not a projection.