@misc{indiciae90f662e4d30a,
  title = {Concepts for reference frames in geodesy and geodynamics - The reference directions},
  author = {Grafarend, E. W. and Richter, B. and Mueller, I. I. and Papo, H. B.},
  year = {1979},
  url = {https://ntrs.nasa.gov/citations/19800027347},
  note = {Source identifier: 19800027347}
}