Full Panorama export with Cesium

Hi,

I am interested to export a 360° full panorama with Cesium. I think this would be a nice feature. There are two main formats for such a panorama.
- Cubemap https://en.wikipedia.org/wiki/Cube_mapping
- Equirectangular https://en.wikipedia.org/wiki/Equirectangular_projection

An easy way to get the panorama would be like the following description:
- Capture 6 images defined by
- Camera position (3D) [works]
- Camera orientation (horizontal and vertical) [works]
- Camera field of view (horizontal and vertical) [wish]
- Merge the 6 images together
- Transform it to an equirectangular panorama https://www.360toolkit.co/convert-cubemap-to-spherical-equirectangular.html

https://twitter.com/zwickmichael/status/1136964139987939328

The definition of the camera field of view is an open issue. I could not find a solution to define that as the other parameters like position, orientation, etc.

The issue names no files, tests, or entry points. Begin by identifying the camera field-of-view and image-capture APIs, then clarify whether cubemap or equirectangular output is required and define acceptance criteria for capturing, merging, and transforming the six images.

Written by the indexing model from the issue text.