50.5.1.2 The initial gravity vector/orientation for the IMU ESKF

Parent: [IMU index](imu index.md), [choice of model for the imu motion model](choice of model-for-the-imu-motion-model.md)

Notes on the initial gravity vector/orientation for the IMU ESKF Solà 2017

• For simplicity, it is assumed that 

• The gravity vector g is estimated in terms of frame q0

• This puts the initial uncertainty on the gravity direction, rather than on the initial orientation.

• Doing this improves linearity, because now the equation is linear in g and the initiial rotation R0 has no uncertainty

• Optional: once g has been initialised, the real horizontal plane is known. If we wish, we could reorient the entire state to this horizontal plane