code: public Vector3d positiveZ(Vector3d dir) {
          dir.x = m10 * m21 - m11 * m20;
          dir.y = m20 * m01 - m21 * m00;
          dir.z = m00 * m11 - m01 * m10;
          return dir.normalize(dir);
      }
docs: /* (non-Javadoc)
  @see org.joml.Matrix3dc#positiveZ(org.joml.Vector3d)