y-based locators subclass from
<code class="docutils literal"><span class="pre">pixel_2d_locator_base</span></code>, a base class that provides most of the interface
required by <code class="docutils literal"><span class="pre">PixelLocatorConcept</span></code>. Users may find this base class useful if
they need to provide other models of <code class="docutils literal"><span class="pre">PixelLocatorConcept</span></code>.</p>
<p>Here is some sample code using locators:</p>
<div class="highlight-cpp"><div clas