cianfa72 said:
A pure rotation KFV about a point evaluated at that point is the null vector.
"Centered" on a particular point is
not the same thing as
evaluated at that point. You need to take a step back and think more carefully.
Take a simpler example: the 2-dimensional Euclidean plane. This manifold has a three-parameter group of KVFs, or at least that's the way it is usually stated. This can be broken up into a two-parameter group of translations and, as it's usually stated, one rotation, corresponding to an SO(2) isometry on the manifold. But let's unpack that further.
Choose standard Cartesian coordinates on the plane, which requires picking one particular point as the origin. That point then becomes the "center" of the SO(2) rotation isometry.
Now write down a basis for the three-parameter group of KVFs consisting of the translations and the rotations centered on the chosen origin. It looks like this:
$$
\partial_x
$$
$$
\partial_y
$$
$$
- y \partial_x + x \partial_y
$$
It should be easy for you to verify that all three of these are KVFs and that they are linearly independent.
Now, looking at the third KVF above, the "rotation" KVF, you can see that it vanishes at the origin, ##(x, y) = (0, 0)##. In other words, if you
evaluate it at the center point of rotation, it vanishes. Or, to put it the way you correctly put it in a previous post, it doesn't "go anywhere" at the center point--it maps the center point to itself. But it doesn't vanish at any
other point, and it obviously induces an isometry on the entire manifold that does
not map every point on the manifold to itself.
Now suppose we decide to look at a rotation about a
different center point, say the point ##(x, y) = (1, 1)##. The KVF that corresponds to
this rotation, in the coordinates we used above, would be:
$$
- (y - 1) \partial_x + (x - 1) \partial_y
$$
This is, as should be evident, a linear combination of all three of the KVFs given above. In other words, it is
not a pure rotation about the center point we chose above, the point ##(x, y) = (0, 0)##. It's a linear combination of a rotation about that point, and two translations (in the ##x## and ##y## directions).