Figure 5.

Motion of the IMU at the mid-stance can be modelled as a rotational motion in a three-dimensional space. The position vector $\mathit{r}$ and angular velocity in laboratory coordinate frame ${\omega }^E$ were computed from the estimated orientation of IMU. Thus, the update velocity ${\breve{\mathit{v}}}^E$ can be recovered as the tangential velocity associated with $\mathit{r}$ and ${\omega }^E.$