Euler pole

The direction of the instantaneous angular-velocity vector describing relative rigid-plate motion on a sphere. At position $\mathbf{r}$, the relative velocity is $\mathbf{\omega }\times \mathbf{r}$. The antipodal pole represents the same physical rotation if the angular-velocity sign is reversed.

Relative angular velocities add as vectors: ${\mathbf{\omega }}_{B/C}={\mathbf{\omega }}_{B/A}+{\mathbf{\omega }}_{A/C}$. Geographic pole latitudes and longitudes must first be converted into Cartesian vector directions.