  The parameters of the Galactic spiral wave are re-determined using a modified
periodogram (spectral) analysis of the galactocentric radial velocities of 58
masers with known trigonometric parallaxes, proper motions, and line-of-site
velocities. The masers span a wide range of galactocentric distances,
$3<$R$<14$ kpc, which, combined with a large scatter of position angles
$\theta$ of these objects in the Galactic plane XY, required an accurate
account of logarithmic dependence of spiral-wave perturbations on both
galactocentric distance and position angle. A periodic signal was detected
corresponding to the spiral density wave with the wavelength $\lambda=2.4 \pm
0.4$ kpc, peak velocity of wave perturbations $f_R=7.5 \pm 1.5$ km s$^{-1}$,
the phase of the Sun in the density wave $\chi_\odot=-160 \pm 15^\circ$, and
the pitch angle of $-5.5 \pm 1^\circ$.
