centered at the origin). In this case, however, the affine
transformation $(A,T)$ is determined only up to a rotation $(AR,
T)$. &gt;When this ambiguity exists and an affine transformation $(A,T)$
needs to be selected, it is customary to choose $R$ such that the Y
axis of the image is mapped onto itself (see below).</p>

<h1 id="id-642">Converting between frame types</h1>

<p>The function <code/>vl_frame2oell</code> can be used to convert any
frame type to an oriented ellipse.</p>

<p>Since all oriented fra