  We present a new self-consistent and versatile method that derives
photospheric radius and temperature variations of Type II-Plateau supernovae
based on their expansion velocities and photometric measurements. We apply the
method to a sample of 26 well-observed, nearby supernovae with published light
curves and velocities. We simultaneously fit ~230 velocity and ~6800 magnitude
measurements distributed over 21 photometric passbands spanning wavelengths
from 0.19 to 2.2 microns. The light curve differences among the Type II-Plateau
supernovae are well-modeled by assuming different rates of photospheric radius
expansion, which we explain as different density profiles of the ejecta and we
argue that steeper density profiles result in flatter plateaus, if everything
else remains unchanged. The steep luminosity decline of Type II-Linear
supernovae is due to fast evolution of the photospheric temperature, which we
verify with a successful fit of SN1980K. Eliminating the need for theoretical
supernova atmosphere models, we obtain self-consistent relative distances,
reddenings, and nickel masses fully accounting for all internal model
uncertainties and covariances. We use our global fit to estimate the time
evolution of any missing band tailored specifically for each supernova and we
construct spectral energy distributions and bolometric light curves. We produce
bolometric corrections for all filter combinations in our sample. We compare
our model to the theoretical dilution factors and find good agreement for the B
and V filters. Our results differ from the theory when the I, J, H, or K bands
are included. We investigate the reddening law towards our supernovae and find
reasonable agreement with standard R_V ~ 3.1 reddening law in UBVRI bands.
Results for other bands are inconclusive. We make our fitting code publicly
available.
