vtkPropPicker in VTK 9.1 is now returning wrong world coordinates.

Thanks for the suggestion. Yes, using locators is one of the options we are considering to speed up picking. It requires some extra bookkeeping and hardware-based picking could be still faster. Therefore, if VTK hardware pickers could be improved to pick on semi-transparent meshes (pick the point wherever the opacity reaches the specified threshold) then that may be a simpler solution for us.