How to solve GGX roughness from existing maps

Question

I have a problem that I cannot really wrap my head around.

I have a minimal light stage setup to scan heads:

I have cross polarized cameras and parallel polarized cameras. I have parallel polarized LEDs I capture k-frames and tracking frames I am able to:

• calculate normals and color albedos from Photometric Stereo (Woodham)
• calculate a mesh via Photogrammetry
• project normals, albedo and appearance on the mesh
• create a reflectance map (via parallel - cross) Does anybody have a tip?

Thank you for your time!