title: What is endpoint error between optical flows?
body: <p>I've seen endpoint error (EPE) used as a metric for determining how close a flow estimation is to a ground truth flow, but I have a few questions about it and was hoping someone could enlighten me:</p>
  
  <ul>
  <li>What does it actually represent?</li>
  <li>How do you calculate it?</li>
  <li>Why is it used?</li>
  </ul>