def test_cartesian_to_sphere(): """Test helper transform function from cartesian to sphere""" x, y, z = (1, 0, 0) # expected values are (0, 0, 1) hypotxy = np.hypot(x, y) r = np.hypot(hypotxy, z) elev = np.arctan2(z, hypotxy) az = np.arctan2(y, x) coord = _cartesian_to_sphere(x, y, z) assert_equal(coord, (az, elev, r)) assert_equal(coord, (0, 0, 1))