Short version:

The following movie shows what's possible with yt-dev ~2.1
The camera rotates about z axis of the data with a constant azimuthal angle w.r.t the z of the data:
curl -O

The following movies shows what happens now if I have a rotation vector or no rotation vector

Weird camera rotation:
curl -O 
Camera rotates about the "up" axis of the camera:
curl -O

Long version:

I brought this issue up a while back but got distracted before it was resolved, and over past two days did more digging/testing.


I cannot rotate the camera about the z axis of the data while keeping the azimuthal angle constant anymore, where as I could do this before in I believe yt-dev 2.1ish.  

What I tried/found:

I thought I mailed the dev list but couldn't dig it out of the yt-dev archive, so maybe I only complained in IRC before.  This thread is the latter portion where Nathan and Sam were helping me with helpful suggestions and what to try.
The example script Sam provided (by not specifying the north_vector) will rotate the camera about the camera's z (up) axis, but not the data's z axis, if looking at the image, what I am trying to do is have the camera rotate around the disk about the axis normal to the disk's plane (assume disk is in x-y plane).

I tried playing with the north_vector, steady_north in the camera object, and the rot_vector in cam.rotation, made sure the vectors are normalized.

I found that if I specify the normal vector (usually designated "L" in example scripts) as the x or -x axis, and the north vector as the z axis, I can look at the data cube (in this case Enzo data), and watch it rotate about the z axis, the behavior I expected.  However, if my L is tilted not 90 degrees (non x or y axis), no matter what I specify as the north vector, the rotation angle changes and the cube wobbles or precesses.

I've modified Sam's script to image the entire box, because it's harder to see the effect if we're looking at a sphere
This script will produce the strange rotation, if the rot_vector is taken out on line 17, then the rotation about the camera up is recovered.  But that's not what was done before and not what I wanted.

I also wrote the script to reproduce the effect I wanted with the rotation, but this is a lot more work than before.  I have to specify a new L and a new up angle for the camera for every frame to get back the effect I wanted.

Hope this help track down the problem, cam.rotation is so much simpler to use :-)