  Rotation is ubiquitous among massive stars. With rotation comes a deformation
to the surface geometry, which in turn leads to alterations in the distribution
of parameters across the surface including surface gravity, temperature and
ionization balance of surface elements. Often, these 3D effects are neglected
when analyzing spectra of rapidly rotating massive stars. We aim to determine
whether neglecting the 3D deformations resulting from rapid rotation has an
impact on the final spectroscopic observables, and if so to what degree. Using
the SPAMMS code, we generate a grid of synthetic spectra that account for the
3D geometry of rapidly rotating stars and compare them to synthetic spectra
generated assuming spherical geometry. Using equivalent width and full width
half maximum measurements as proxies, we determine how the measured
temperature, helium abundance and projected rotation rates of individual lines
in different ionization states vary with rotation rate and inclination. We find
that the 3D geometry can have a significant impact on the measured parameters.
We show that the temperature is highly dependent on both the rotation rate and
the inclination, and that the same system viewed at different inclinations can
have measured temperatures that differ by as much as 10\%. We also find that
the helium abundance can be underestimated by as much as 60\%, and that lines
in different ionization states can have measurable differences in rotation
rates. We demonstrate that these differences in rotation rates can be seen in
observed data and show that this could allow for an inclination independent
measurement of the rotational velocity. Our results indicate that neglecting
the 3D effects of rotation can cause significant biases in the measured
spectroscopic parameters, and that in many cases, the measured values are more
than 3$\sigma$ away from the true values.
