Hi @southpole ,
Thanks for your post and welcome to the Cesium community.
Are you referring to the distorted circle sector appearance of the imagery or the fact that the path of circles you are plotting is straight but then bends as it gets closer to the poles?
In terms of the circle sector appearance, what you are seeing is that imagery is not rendered at the poles. This is because there are distortions involved in projecting equirectilinear projections (Geographic/WebMercator) to a sphere. And in fact most imagery comes with holes at the poles due to this distortion. What would be needed to solve this is support in cesium for polar stereographic projection, which we do not have but would be very cool to add. Here are two previous threads discussing this topic Render Polar Imagery & Having trouble implementing Polar Stereographic Projection for Imagery Provider.
If the bend in your path is unexpected and your question pertains to that, would writing some code to reproduce it using our sandcastle tool? https://sandcastle.cesium.com/ This will help us more efficiently investigate the issue.
Thanks,
Luke