  We present a formalism for analyzing galaxy clustering on the lightcone with
the 2-point correlation in the Spherical Fourier-Bessel (SFB) formalism, which
is a natural choice to account for all wide-angle and relativistic (GR)
effects. We extend previous studies by including all projection and GR effects,
developing an efficient numerical implementation that avoids the use of the
Limber approximation, includes multi-bins correlations and a full non-diagonal
covariance.
  Using this formalism, we investigate the impact of neglecting GR corrections,
and in particular how much this could bias measurements of the non-Gaussianity
parameter $f_\mathrm{NL}$.
  Our results show that not including relativistic projection terms can
systematically and non-negligibly bias estimates of $f_\mathrm{NL}$. The exact
results depend on survey specifications and galaxy population properties, but
we stress that a bias will generally be present.
  Finally, we develop a novel prescription for cross-bin correlations that
allow to search for a clean signal of relativistic corrections, and show that
this requires the use of the 3D full-sky formalism.
