title: When should these methods be used to calculate blob orientation?
body: <p>In image processing, each of the following methods can be used to get the orientation of a blob region:</p>
  
  <ol>
  <li>Using <a href="https://en.wikipedia.org/wiki/Image_moment" rel="nofollow noreferrer">second order central moments</a></li>
  <li>Using <a href="https://alyssaq.github.io/2015/computing-the-axes-or-orientation-of-a-blob/" rel="nofollow noreferrer">PCA</a> to find the axis</li>
  <li>Using <a href="https://en.wikipedia.org/wiki/Distance_transform" rel="nofollow noreferrer">distance transform</a> to get the skeleton and axis</li>
  <li>Other techniques, like fitting the contour of the region with an ellipse.</li>
  </ol>
  
  <p>When should I consider using a specific method? How do they compare, in terms of accuracy and performance?</p>