  The spectra from Fe-peak elements may be used to determine the temperature
and density of various astrophysical objects. Determination of these quantities
is underpinned by the accuracy and the comprehensiveness of the underlying
atomic structure and collisional calculations. In the following paper, we shall
focus specifically on Ni IV lines associated with transitions amongst several
low-lying levels. We shall employ modified versions of the parallel Dirac
R-matrix codes, considering both electron-impact excitation of Ni$^{3+}$ and
the photoionisation of both the ground and excited states of Ni$^{2+}$. We
produce high-quality data sets for both processes, and using these data, we
calculate line ratios relevant for plasma diagnostics of temperature and
density.
