mes are special cases of oriented ellipses,
this transformation is trivial for oriented circles and ellipses. On
the other hand, rewriting unoriented frames as <em>oriented</em>
ellipses requires assigning (arbitrarily) an orientation to them.</p>

<p>By default, when an arbitrary orientation has to be selected in the
conversion, this is done in such a way that the affine transformation
$(A,T)$ is <em>upright</em>. This means that $A$ maps the Y axis to
itself:</p>

\[
  A\begin{bmatrix}1\\ 0\end{bmatrix} \