title: OpenCV: At what index do Mat objects start?
body: <p>I understand that the <code>Mat</code> in OpenCV follows the mathematical convention of the order of the row and the col parameter, which is row first and col second. But how about the start index? Is it 0 like in informatics or 1 like the maths?</p>
  
  <p>Moreover, is the convention for the start index consistent over all the methods, most prominently <code>at&lt;_Tp&gt;()</code>, <code>rowRange()</code>, and <code>colRange()</code>?</p>
  
  <p>Just a note for myself:</p>
  
  <pre><code>Mat m = ...;
  Vec4b e = m.at&lt;Vec4b&gt;(        i, j ); // equivalent to next line (note swapped i and j)
  Vec4b e = m.at&lt;Vec4b&gt;(Point2i(j, i));
  </code></pre>