  We present a new method for determining physical parameters of RRab variables
exclusively from multicolour light curves. Our method is an Inverse Photometric
Baade-Wesselink analysis which, using a nonlinear least squares algorithm,
searches for the effective temperature (T_eff) and pulsational velocity (V_p)
curves and other physical parameters that best fit the observed light curves,
utilising synthetic colours and bolometric corrections from static atmosphere
models. The T_eff and V_p curves are initially derived from empirical relations
then they are varied by the fitting algorithm. The method yields the variations
and the absolute values of the radius, the effective temperature, the visual
brightness, and the luminosity of individual objects. Distance and mass are
also determined. The method is tested on 9 RRab stars subjected to
Baade-Wesselink analyses earlier by several authors. The physical parameters
derived by our method using only the light curve data of these stars are well
within their possible ranges defined by direct Baade-Wesselink and other
techniques. A new empirical relation between the I_C magnitude and the
pulsational velocity is also presented, which allows to construct the V_p curve
of an RRab star purely from photometric observations to an accuracy of about
3.5 km/s.
