[yt-users] a question on camera with volume rendering

Hi, I think I am unclear about the orientation in pf.h.camera(c,W,L, ..., north=vec, ...). I got some nice looking pictures but don't know what north means in this case, because when I switch north=vec to north=reverse of vec, the image rotates along the vertical direction, so it seems like north is pointing to either left or right. It is very desirable for me to be able to make sure which direction vec points to (vec is the vec in north=vec) in the final rendered plot. Thanks in advance for help, Renyue