Optical Position Measurement with Raspberry Pi Zero

Optical position measurement with a Raspberry Pi Zero & camera. I printed out some circles with an inkjet printer and stuck them on a moving part and a fixed part. I used OpenCV to detect the circle positions (SimpleBlobDetector) and then found the intersection point between lines drawn between the circle centers. It looks like the jitter in the measured position of the beam (left side) relative to the fixed part on the right is below 10 microns. I am recalculating the image scale on each frame, by comparing the known (previously measured), and currently apparent distance between the three dots on the right (indicated with green circles).

[@bru22003]

John, that is just terrific. I want one!!

[@PracticalRobotics]

That's pretty great. I've wondered what kind of OpenCV work could be done with a Zero but haven't tried it. What kind of frame rate have you managed?

[@dancevideo2]

So far I've only used the Pi Zero for recording the raw video, and I'm running OpenCV on a Pi 4, and this is only a few fps right now BUT everything is hugely inefficient as this was a super-rough, first-day try and the code is doing all kind of unnecessary things. Doing it sensibly, like initial detection on a very low resolution frame, and then the full resolution just in a very small window on each pre-detected dot position, I could imagine it being real time at some resolution even on the Zero. Just not sure what resolution that would be.
In my particular application I'm just measuring a creep over hours and days, so I don't need to run the analysis on the Zero at all, let alone in realtime, I was only intending the Zero just for the acquisition.