Vector3d v = pt.pix2vect_ring(nside, pix);
z = v.z;
nring = (int) pt.RingNum(nside, z);
assertEquals("z=" + z, 1, nring, 1e-10);
pix = 11;
v = pt.pix2vect_ring(nside, pix);
z = v.z;
nring = (int) pt.RingNum(nside, z);
assertEquals("z=" + z, 2, nring, 1e-10);
pix = 23;
v = pt.pix2vect_ring(nside, pix);