  In this paper we study pseudo-Riemannian spaces with a degenerate curvature
structure i.e. there exists a continuous family of metrics having identical
polynomial curvature invariants. We approach this problem by utilising an idea
coming from invariant theory. This involves the existence of a boost which is
assumed to extend to a neighbourhood. This approach proves to be very fruitful:
It produces a class of metrics containing all known examples of
$\mathcal{I}$-degenerate metrics. To date, only Kundt and Walker metrics have
been given, however, our study gives a plethora of examples showing that
$\mathcal{I}$-degenerate metrics extend beyond the Kundt and Walker examples.
  The approach also gives a useful criterion for a metric to be
$\mathcal{I}$-degenerate. Specifically, we use this to study the subclass of
VSI and CSI metrics (i.e., spaces where polynomial curvature invariants are all
vanishing or constants, respectively).
