Observational calibration of the projection factor of Cepheids - IV. Period-projection factor relation of Galactic and Magellanic Cloud CepheidsA. Gallenne, P. Kervella, A. Mérand, G. Pietrzyński, W. Gieren, N. Nardetto and B. TrahinA&A, 608 (2017) A18DOI: https://doi.org/10.1051/0004-6361/201731589
