t
is half of the side of the patch domain, a square in
the <a shape="rect" href="covdet.html#tut.covdet.frames">frame reference
frame</a>. Since most detectors latch on image structures (e.g. blobs)
that, in the normalised frame reference, have a size comparable to a
circle of radius one, setting <code/>PatchRelativeExtent</code> to 6
makes the patch about six times largerer than the size of the corner
structure. This is approximately the default extent of SIFT feature
descriptors.</p>

<p>A second importan