  Magnetometry with nitrogen-vacancy color centers in diamond has gained
significant interest among researchers in recent years. Absolute knowledge of
the three-dimensional orientation of the magnetic field is necessary for many
applications. Conventional magnetometry measurements are usually performed with
NV ensembles in a bulk diamond with a thin NV layer or a scanning probe in the
form of a diamond tip, which requires a smooth sample surface and proximity of
the probing device, often limiting the sensing capabilities. Here, we present a
method for determining the three-dimensional orientation of the magnetic field
vector relative to the diamond crystal lattice. We demonstrate that NV centers
in arbitrarily oriented submicrometer-sized diamond powder deposited on a
planar surface can be used for sensing the magnetic field. Our work can be
extended to irregular surfaces, which shows a promising path for
nanodiamond-based photonic sensors.
