How to set the direction vectors in gui.SceneWidget().scene.camera.look_at(center, eye, up)?

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D/issues).
- [X] For Python issues, I have tested with the [latest development wheel](http://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](http://www.open3d.org/docs/release/) and the [latest documentation](http://www.open3d.org/docs/latest/) (for `master` branch).

### My Question

There are two questions which I‘m very confused.

1. If I use **o3d.geometry.get_rotation_matrix_from_quaternion(quaternion)** method to get **rotation matrix**, the quaternion composed by [ox, oy, oz, ow] or [ow, ox, oy, oz]? And the single colomn(or single row) of rotation matrix represent which direction vector?
2. If I want to use rotation matrix to set camera view, what means of center/eye/up vector in gui.SceneWidget().scene.camera.look_at(center, eye, up) python interface? I check the C++ code, and only find [this](https://github.com/isl-org/Open3D/blob/c3dfcbdc8d7cdf5603367b783b6d4a43fc934bd5/cpp/open3d/visualization/utility/GLHelper.cpp#:~:text=GLMatrix4f-,LookAt,-(const%20Eigen%3A%3AVector3d), but I can't understand the means of code.

It will be great if anyone can help to provide relevant instructions.
Thanks in advance!