  In this paper, we employ a general relativistic formalism and develop new
theoretical tools that allow us to analytically express the mass and electric
charge of the Reissner-Nordstr\"{o}m black hole as well as its distance to a
distant observer in terms of few directly observable quantities, such as the
total frequency shift, aperture angle of the telescope, and redshift rapidity.
Our analytic and concise formulas are valid on the midline, and the redshift
rapidity is a relativistic invariant observable that represents the evolution
of the frequency shift with respect to the proper time in the
Reissner-Nordstr\"{o}m spacetime. This procedure is applicable for particles
undergoing circular motion around a spherically symmetric and electrically
charged black hole, which is the case for accretion disks orbiting supermassive
black holes hosted at the core of active galactic nuclei. Although this type of
black hole is expected to be electrically neutral, our results provide a novel
method to measure the electric charge of the Reissner-Nordstr\"{o}m black hole,
hence can shed some light on this claim. Besides, these results allow us to
measure the mass of the black hole and its distance from the Earth, and we can
employ the general formulas in black hole parameter estimation studies.
