1. A concise explanation of the problem you're experiencing.
When I tilt and rotate the 3D map, the direction of the map is unknown
2. A minimal code example. If you've found a bug, this helps us reproduce and repair it.
3. Context. Why do you need to do this? We might know a better way to accomplish your goal.
When we rotate 3D map with terrain, we don't know which direction is pointing up. This is a basic GIS function
4. The Cesium version you're using, your operating system and browser.
Cesium 1.42