Currently, the specific surface area is calculated with a direct method and corrected with a corrective factor (2/3 for spheres).
I have plan to introduce the covariance function (see another issue).
But eventually I would like to have also the marching cube algorithm. That would be probably the best method among the 3 (direct method has overestimation that needs to be corrected, but the corrective factor is particle-shape dependent, so you need to assume the particle shape, and covariance function, while better, requires an isotropy assumption to derive the specific surface area which is not true for every material).

I labeled this issue "help wanted" because:

• I have no experience with the marching cube algorithm and don't have the time (other priorities) to develop it
• Specific surface area is low priority (surface area being a fractal I do not consider its value so important from characterization, better to fit it eventually).
• I would be very glad if someone could contribute on this one! (as a reminder, if you are willing to add your contribution you will be credited of course)