eatures are
estimated to be upright by default (formally, this means that the
affine transformation $(A,T)$ maps the vertical axis $(0,1)$ to
itself).</p>

<p>Estimating and removing the effect of rotation from a feature frame
is needed in order to compute rotationally invariant descriptors. This
can be obtained by specifying the <code/>EstimateOrientation</code>
option:</p>

<div class="highlight"><pre><span class="n">frames</span> <span class="p">=</span> <span class="n">vl_covdet</span><span class="p">(<