UPDATE: I added defaults and a config file where you can save your settings. See lines 19 and 40 in the new code.
Fooling around with OpenCV and Python to measure stuff with a single camera. Automatic for the people. Try it out: https://gitlab.com/duder1966/youtube-projects/-/tree/master/OpenCV/camruler
Camera: https://youtu.be/qf-PKqFhwMg