  The negatively charged nitrogen-vacancy (NV-) centre in diamond has many
exciting applications in quantum nano-metrology, including magnetometry,
electrometry, thermometry and piezometry. Indeed, it is possible for a single
NV- centre to measure the complete three-dimensional vector of the local
electric field or the position of a single fundamental charge in ambient
conditions. However, in order to achieve such vector measurements, near
complete knowledge of the orientation of the centre's defect structure is
required. Here, we demonstrate an optically detected magnetic resonance (ODMR)
technique employing rotations of static electric and magnetic fields that
precisely determines the orientation of the centre's major and minor trigonal
symmetry axes. Thus, our technique is an enabler of the centre's existing
vector sensing applications and also motivates new applications in multi-axis
rotation sensing, NV growth characterization and diamond crystallography.
