# How to measure distance along solvent-accessible surface of protein complex in PDB file?

I am looking for a straightforward way to measure the distance between two active sites in a protein complex (PDB file). I need the distance along the solvent-accessible surface of the protein and not the linear distance that would go through the protein, and which the distance wizard will give.

I would prefer a solution using PyMOL, although I would consider alternatives as well.

A suitable measuring size would probably be in the order of $${\sim}\pu{10^{-11} m}$$ or $$1/10$$ the size of an carbon atom.