  We show that uniaxial color centers in silicon carbide with hexagonal lattice
structure can be used to measure not only the strength but also the polar angle
of the external magnetic field with respect to the defect axis with high
precision. The method is based on the optical detection of multiple spin
resonances in the silicon vacancy defect with quadruplet ground state. We
achieve a perfect agreement between the experimental and calculated spin
resonance spectra without any fitting parameters, providing angle resolution of
a few degrees in the magnetic field range up to several millitesla. Our
approach is suitable for ensembles as well as for single spin-3/2 color
centers, allowing for vector magnetometry on the nanoscale at ambient
conditions.
