What I don't get is why this isn't easy to do with a smartphone. A little motorized turntable with a stand for your phone and a calibration object covered in tracking symbols to use for adjusting the input from the camera. Why is that so impossible?
Not the best example but this http://koanlabs.org/vignettes.html rock is ~5 cm tall and my best guess is the minimum detectable feature size is about 10 microns.
EDIT: Sorry to be clear the definition of easy here is "as easy as most photogrammetry", to get good results you will universally do a lot of knob twiddling, waiting and cleaning up broken bits of mesh unless all you do is scan rocks. Scanning rocks is easy.
"The devil is in the details" and "talk is cheap" are common expressions for a reason
But I have found that smartphones give very inconsistent results (probably due to image"improving" algorithms...), see https://www.instagram.com/p/B1q1syMoHfG/
So I moved on to the raspberry pi + camera, which is much easier and better to control as you need very, very consistent images...
It worked surprisingly well, but was unfortunately discontinued. Since it was cloud based the app no longer works :(
I wonder if there are any similar apps available now?