From the three previous posts on the topic (Lengths of digital curves, parts 1, 2, 3) and a little presentation I gave recently I created an article for the wiki. In comparison, analysis is more extensive and there are more illustrations. At the end there are two examples of computation of roundness with Pixcavator 2.4. Circles have roundness close to 90, squares close to 80. It works quite well for large objects. You can now distinguish between circles and squares and between squares and elongated objects. For example, you have now a new way to automatically count (round) cells in the image and ignore (rough edged) noise.