Why use ellipsoids instead of regular spheres in Cesium?

Why use ellipsoids instead of regular spheres in Cesium?As is well known, using an ellipsoid results in greater computational complexity. Would using a regular sphere like Mapbox be a better solution?

Hi @xingrui94 - perhaps it’s about the birth of Cesium - it seems like it was a project for NASA - as you know, it’s closer to technology and science than to games and arts. Here I’ll recall a bit from my education - our planet is not very smooth - it’s more like a crooked apple - its radius is not constant and can differ by hundreds of kilometers - thus, an ellipsoid would be more suitable than simple figures - the next stage - apply deformations for a very general approximation over thousands of kilometers - did you know that there is a trench more than 10 kilometers deep in the Indian Ocean and conversely in the North Atlantic, there’s a hill slightly higher (not in ground - sea level)? Our poles are also depressed like on an apple by several kilometers. Thus, it already starts to differ significantly from a sphere - and if you will need image more realistic then in a game or a movie - but as sample for applications like displaying trajectories of spacecraft, air, drones, seaships, trains - may be you can agree that an error even by 1 kilometer above or below the earth is critical. What to say when the difference can be tens or hundreds of kilometers? I think it would be great to build a sphere of the average radius of the planet (6400 km) and compare intersections with the spheroid. I hope I managed to explain that it’s not just developers’ games out of boredom.

Nice sample image, you can see here:
And here:
Have a nice day.