Any books or papers tell how to draw a hollow circle fan on a surface of ellipsoid?

CesiumJS
1

Hi,All,

I am not good at math. However, I have to create a “Hollow Circle Fan”, see attachment, on Cesium global. I read the code of “computeEllipseBoundary”. Totally lost in it.

I know there is an algorithm for circle creating on book “Computer Graphics with OpenGL”. But, it’s not on a ellipsoid.

Are there any books or papers talk about this?

Thanks,

-Jonathan

fh.jpg

2

Hi Jonathan,

We have this on the roadmap (it is the “sector geometry”); however, it will be at least a few months before we get to it as we focus on stabilizing the Cesium API.

Our implementation will use arc distance for the inner and outer radii, which requires an iterative solution. If you are OK with a less precise solution, you could do the computation on a tangent plane using [(cos(theta), sin(theta) * r] for both radii then join each arc. We use a tangent plane for polygon triangulation, see createGeometryFromPositions in PolygonGeometry.js. Again, I wouldn’t use a tangent plane here, but it might be good enough depending on your use case.

Patrick