Welcome to the community! 
Thank you for the screenshot - I can clearly see that the rock extrudes above the surface of the earth. It seems like this might be problematic if you are drawing a polyline on 3D Tiles from a birds-eye view. What kind of functionality are you looking for?
-Sam
I have received your reply.In fact, I just want to cross the line formed by these green balls and stick to the rock(inside the yellow circle)，There is also an issue for a similar problemPolylines slice through 3D Tiles rather than draping over them.
I think it’s because of the design pattern of clampToGround itself. I want to know how to start if I want to modify it.Thanks very much!
We always encourage community engagement through code contributions. If you are able to, we would love it if you submitted a pull request addressing the issue that you mentioned!
If you submit a pull request, I can help coordinate with the rest of the Cesium development team to ensure that it is reviewed in a timely manner.
I am not very familiar with the design of clampToGround. Thus, I currently do not have any specific suggestions for how to begin development. I will continue to look over this part of the codebase in the upcoming days. Maybe other community members can interject with some suggestions here? Let me know if you have any other questions or concerns!
Best,
Sam