Cesium applies this angle across the frame's longer axis, so it is the
horizontal FOV for landscape photos and the vertical FOV for portrait
ones. The unambiguous vertical angle is shown below and is what gets saved.
Optional — derive FOV from real camera specs instead of guessing:
Sensor width means the sensor dimension along the photo's horizontal
axis. A full-frame camera is 36mm held landscape, but 24mm rotated for a
portrait shot.
↳ FOV derived from focal length + sensor size