  Through an innovative combination of multiple observing techniques and mod-
eling, we are assembling a comprehensive understanding of the pulsation and
close environment of Cepheids. We developed the SPIPS modeling tool that
combines all observables (radial velocimetry, photometry, angular diameters
from interferometry) to derive the relevant physical parameters of the star
(effective temperature, infrared ex- cess, reddening,...) and the ratio of the
distance and the projection factor d/p. We present the application of SPIPS to
the long-period Cepheid RS Pup, for which we derive p = 1.25 +/- 0.06. The
addition of this massive Cepheid consolidates the existing sample of p-factor
measurements towards long-period pulsators. This allows us to conclude that p
is constant or mildly variable around p = 1.29 +/- 0.04 (+/-3%) as a function
of the pulsation period. The forthcoming Gaia DR2 will provide a considerable
improvement in quantity and accuracy of the trigonometric parallaxes of
Cepheids. From this sample, the SPIPS modeling tool will enable a robust
calibration of the Cepheid distance scale.
