  Galactic Cepheids are necessary tools for calibrating the period-luminosity
relation, but distances to individual Galactic Cepheids are difficult to
precisely measure and are limited to a small number of techniques such as
direct parallax, main-sequence fitting to open clusters that host Cepheids and
Baade-Wesselink (BW) methods. In this work, we re-examine the application of
Wesenheit function in determining distances to more than 300 Galactic Cepheids,
by taking advantage of the fact that the Wesenheit function is extinction free
by definition. The Wesenheit distances were used to calibrate the projection
factor (p-factor) for Galactic Cepheids that also possess BW distances. Based
on ~70 Cepheids, we found that a period-p factor relation may exhibit a
non-linear trend with a considerable scatter. During our investigation,
discrepant p factors for delta Cephei were found in the literature. This may be
due to inconsistent measurements of the angular diameters using different
empirical techniques. We discuss the reason for the inconsistency of angular
diameter measurements and offer a possible remedy for this problem.
