  The diameter of a star is a major observable that serves to test the validity
of stellar structure theories. It is also a difficult observable that is mostly
obtained with indirect methods since the stars are so remote. Today only ~600
apparent star diameters have been measured by direct methods: optical
interferometry and lunar occultations. Accurate star diameters are now required
in the new field of exoplanet studies, since they condition the planets' sizes
in transit observations, and recent publications illustrate a visible renewal
of interest in this topic.
  Our analysis is based on the modeling of the relationship between measured
angular diameters and photometries. It makes use of two new reddening-free
concepts: a distance indicator called pseudomagnitude, and a quasi-experimental
observable that is independent of distance and specific to each star, called
the differential surface brightness (DSB). The use of all the published
measurements of apparent diameters that have been collected so far, and a
careful modeling of the DSB allow us to estimate star diameters with a median
statistical error of 1%, knowing their spectral type and, in the present case,
the VJHKs photometries.
  We introduce two catalogs, the JMMC Measured Diameters Catalog (JMDC),
containing measured star diameters, and the second version of the JMMC Stellar
Diameter Catalog (JSDC), augmented to about 453000 star diameters. Finally, we
provide simple formulas and a table of coefficients to quickly estimate stellar
angular diameters and associated errors from (V, Ks) magnitudes and spectral
types.
