rotate.horizontal was actually my second attempt at a shot such as this. My first, rotate.vertical, was along the same lines: rotating the camera while staying on a fixed axis. The problem with rotate.vert was that the Mini Pro 4 will not go straight up while rotating. dji engineers are aware of the issue, but it's not a priority.

 

(If you want to see rotate.vertical and how it failed, head over to the YouTube page.)