I am confused about the sign on linear acceleration. Experimenting around it seems that the vector is expressed in the chosen coordinate frame, but it is the inverse of what I expect. So, for example, if I am using the default frame and with the camera horizontal, I would expect that y = 9.8 since y points down in the default frame, but instead I get y = -9.8. This seems to be consistently true no matter what coordinate frame I use (i.e., that the sign is reversed from what I expect). I am sure it is something silly that I am missing, or am thinking about things in the wrong way.