'Find rotation and translation to fit all 3 fiducials.'

def fit_fiducials(self):

    src_fid = np.vstack((self.hsp.lpa, self.hsp.nasion, self.hsp.rpa))
    src_fid -= self.hsp.nasion
    tgt_fid = np.vstack((self.mri.lpa, self.mri.nasion, self.mri.rpa))
    tgt_fid -= self.mri.nasion
    tgt_fid *= self.scale
    x0 = (self.rot_x, self.rot_y, self.rot_z, self.trans_x, self.trans_y, self.trans_z)
    est = fit_matched_points(src_fid, tgt_fid, x0=x0, out='params')
    (self.rot_x, self.rot_y, self.rot_z) = est[:3]
    (self.trans_x, self.trans_y, self.trans_z) = est[3:]
