to achive this picture you have to preform an EPR experiment. You start by placing you sample into the EPR cavity and by taking the the EPR pattern. It is important that you place sample in the cavity with the external magnetic field of the EPR machine is according to for example the OO1 direction of the lattice. After taking the EPR pattern you can calculate the g values for the 3 principal directions of the sample for that orientation with respect to the extrenal field. You repeat this experiment but now you rotate the sample relative to the external magnetic field. This leads again for g values for the 3 principale directions. If you do this for different orientations, you get the figure.