problems in RT_line_fine_opacity() ?
Looking at the code of RT_line_fine_opacity(), I think that the min() on line 333 (r9907) should probably be a max() to allow the line to occupy the full grid. That would be pretty extreme though, so I wonder if that branch is ever taken?
But on a more fundamental level. How does the fine grid work? I do not see any anu[] array similar to the coarse grid. I do see rfield.fine_opac_velocity_width which suggest that the mesh is filled using constant resolving power (similar to the coarse grid). However, the code on line 352 does a linear fill, which implies that the mesh has a constant frequency step rather than a constant velocity width... For lines with huge damping wings this could be an issue.