Sensing: linear acceleration

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.


Hi bblumberg,

What actually measured by the imu in its simplest form is a_measured = a - g, where a is the actual acceleration of the camera. So when the camera is static, the imu always returns -g. That’s why you get y = -9.8 in the default frame.

hope it will help you.