An in-Blender solution would be preferred so I don't have to switch programs, but other tools are welcome too.
I'm testing out face rigging via Blender's built-in Rigify plugin, and it suggests defining a pivot based on a spherical shape. However, I only have a small-curvature concentric-ring mesh per eye on my test model (it's imported from a program that generally doesn't use complete spheres for eyes). Is there a way I can calculate the center of the would-be sphere using just the irises? Thanks!