Hi, Olivier,
it's been ages that I used Photoscan (not because it's bad, but simply because of dev requirements) - so I cannot tell for sure if Photoscan has a world-lock-function like RealityCapture.
The idea is this: When you do photogrammetry, the points in space you get have no “origin”, even if you have a metric cube in your scanned scene, you first have to tell your pipeline, which points (on the cube) belong to the reference system. In RC this is what ground points are for: By defining points (2d on images, relating to 3d in the point cloud) to sit at given coordinates in your world space, the model you get “simply” gets rotated/scaled/transformed to that universe. Actually, it doesn't get transformed, it's just that the point coordinates are matched up.
In your case - with a rotating object - you'd need to adjust the reference (world space) accordingly, meaning, you'd need to rotate the rock in a “known way”, so that your ground points rotate along. I'm certain that photoscan has something like this “hidden somewhere”
Since this *should* be part of any photogrammetry pipeline that works with “interlocking” meshes (aligning from one scan to another or, bob beware, even combining Lidar with Ph*metry), aligning meshes - in theory - “is part of the process”.
(I say “in theory”, because in reality ph*metry comes with its own pitfalls in terms of large-model-precision (floating point issues, from my perspective, being the most likely reason).)
Marc