  We present a new luminosity-colour relation based on trigonometric parallaxes
for thin disc main-sequence stars in SDSS photometry. We matched stars from the
newly reduced Hipparcos catalogue with the ones taken from 2MASS All-Sky
Catalogue of Point Sources, and applied a series of constraints, i.e. relative
parallax errors ($\sigma_{\pi}/\pi\leq0.05$), metallicity
($-0.30\leq[M/H]\leq0.20$ dex), age ($0\leq t \leq 10$ Gyr) and surface gravity
($\log g>4$), and obtained a sample of thin disc main-sequence stars. Then, we
used our previous transformation equations (Bilir et al. 2008a) between SDSS
and 2MASS photometries and calibrated the $M_{g}$ absolute magnitudes to the
$(g-r)_{0}$ and $(r-i)_0$ colours. The transformation formulae between 2MASS
and SDSS photometries along with the absolute magnitude calibration provide
space densities for bright stars which saturate the SDSS magnitudes.
