**I am playing with rotations around the globe.
I would like to know if there is a way to get the UP of a point on the map.
By that I mean, if I go to a lat/long, the up would be the direction of the sky.
Thank you**

The problem is I have a model, and a camera, the camera will be attached on the model like a TPS. The model got a rotation from a server, but the server just give the rotation of the model himself, without reference.

So I would like to get the normal vector of the tangeant of the map (ellipsoid ?) so I can use that up coordinate to calculate the rotation of the model

There’s a couple of ways you can do this. This is what the Transforms.easyNorthUpToFixedFrame (https://cesiumjs.org/Cesium/Build/Documentation/Transforms.html?classFilter=Transforms#.eastNorthUpToFixedFrame) is for. This will create a transformation matrix for any given location on the Earth such that positive Z is in the direction of up, away from the ground.

The other way is to convert your cartesian3 point to a cartographic point. Increasing the height will always be in the direction you expect. This is how this Sandcastle offsets any tileset up/down regardless of where it is on the globe:

https://cesiumjs.org/Cesium/Apps/Sandcastle/index.html?src=3D%20Tiles%20Adjust%20Height.html

Let me know if this helps!

Thank you Omar, this was very helpful