title: Two parallel line segments intersection
body: <p>I know there are many algorithms to verify whether two line segments are intersected.</p>
  
  <p>The line segments I'm talking about are length line constructed by 2 end points.</p>
  
  <p>But once they encountered parallel condition, they just tell the user a big "No" and<br/>
  pretend there is no overlap, share end point, or end point collusion.</p>
  
  <p>I know I can can calculate the distance between 2 lines segments.<br/>
  If the distance is 0, check the end points located in the other line segments or not.<br/>
  And this means I have to use a lot of if else and &amp;&amp; || conditions.</p>
  
  <p>This is not difficult, but my question is</p>
  
  <p><strong>"Is there a trick( or mathematics) method to calculate this special parallel case?"</strong></p>
  
  <p><strong>I hope this picture clarify my question<br/>
  <a href="http://judark.myweb.hinet.net/parallel.JPG" rel="nofollow noreferrer">http://judark.myweb.hinet.net/parallel.JPG</a></strong></p>