Lifting of ${\mathbb{R}\mathbb{P}}^{d-1}$-valued maps in $BV$ and applications to uniaxial $Q$-tensors. With an appendix on an intrinsic $BV$-energy for manifold-valued maps

We prove that a $BV$ map with values into the projective space ${\mathbb{R}\mathbb{P}}^{d-1}$ has a $BV$ lifting with values into the unit sphere ${\mathbb{S}}^{d-1}$ that satisfies an optimal $BV$-estimate. As an application to liquid crystals, this result is also stated for $BV$ maps with values into the set of uniaxial $Q$-tensors. In order to quantify $BV$ liftings, we prove an explicit formula for an intrinsic $BV$-energy of maps with values into any compact smooth manifold.