code: def Rz_to_uv(R,z,delta=1.,oblate=False):
      
      coshu, cosv= Rz_to_coshucosv(R,z,delta,oblate=oblate)
      u= sc.arccosh(coshu)
      v= sc.arccos(cosv)
      return (u,v)
docs: NAME:
  
         Rz_to_uv
  
      PURPOSE:
  
         calculate prolate or oblate confocal u and v coordinates from R,z, and delta
  
      INPUT:
  
         R - radius
  
         z - height
  
         delta= focus
  
         oblate= (False) if True, compute oblate confocal coordinates instead of prolate
  
      OUTPUT:
  
         (u,v)
  
      HISTORY:
  
         2012-11-27 - Written - Bovy (IAS)
  
         2017-10-11 - Added oblate coordinates - Bovy (UofT)