How does the spherical gantry account for the shadows that the arm and camera casts on the object as the gantry moves round to take photographs?
I guess it will twist the joints to be in a special position to avoid making changes to light approaching the object, but I am also wondering if the light landing on the gantry has reflection and change the light field.
Yes! This can be a tricky engineering problem. They try their best to design these systems so that for every lighting and camera position the arms can be moved into a position where they do not cast a shadow. A different approach that is quite popular is to use multiple cameras and lights arranged on a dome to avoid shadow issues, here is an example - https://ict.usc.edu/prototypes/light-stages/#gallery-1
@SainanChen Often people will wrap the arms in black fabric or paint them matte black to avoid reflections.