# Tag Info

The accelerometer measures the gravity vector in the body frame, call it $a$. If you normalize that, say $\hat a$, it's the third row of the rotation matrix $R$ that represents the rotation of the body. i.e. $$R^\top \begin{pmatrix}0 \\ 0 \\ 1\end{pmatrix} = \frac{a}{||a||} = \hat a = z_{\mathcal{W}}^{\mathcal{B}}$$ So  R = \begin{pmatrix} ? \\ ? \\ \...