  This paper considers the problem of estimating the position and orientation
of a user equipped with a three-dimensional (3D) array receiving downlink
far-field THz signals from multiple base stations with known positions and
orientations. We derive the Cram\'er-Rao Bound for the localization problem and
define the coverage of the considered system. We compare the error lower bound
distributions of the conventional planar array and the 3D array configurations
at different user equipment (UE) positions and orientations. Our numerical
results obtained for array configurations with an equal number of elements show
very limited coverage of the planar-array configuration, especially across the
UE orientation range. Conversely, a 3D array configuration offers an overall
higher coverage with minor performance loss in certain UE positions and
orientations.
