Convert between rhombohedral and hexagonal cells

Convert between Rhombohedral and Hexagonal cells

Rhombohedral
cell parameters:
Hexagonal
cell parameters:
cell dimensions : a=b=c cell dimensions : a=b
angles :                             :  c
alpha=beta=gamma: angles alpha=beta=90, gamma=120
R. Volume : H. Volume(3x R.V) :

Reindex from an R-cell (hkl) to a hexagonal cell (HKL):

Conditions limiting possible reflections: