Model.make_valid_pdb_coordinates() — make coordinates fit in PDB format

make_valid_pdb_coordinates()
This command ensures that all of the model's coordinates can be written out to a PDB file. Since the PDB format is fixed width, there is a maximum size beyond which x, y or z coordinates cannot be represented; they cannot be smaller than -999.999 or larger than 9999.999. This command ensures that the coordinates lie in this range by simply reflecting them if necessary.