\anchor free_borders_anchor
<h2>Sew free borders</h2>
-This functionality allows you to unite two free borders of a 2D mesh.
+This functionality allows you to unite free borders of a 2D mesh.
+
+There are two working modes: \a Automatic and \a Manual. In the \b
+Automatic mode, the program finds free borders coincident within a
+certain tolerance and sew them. Optionally it is possible to adjust
+the found free borders before sewing. In the \b Manual mode you are to
+define borders to sew by picking three nodes of each border.
\image html sewing1.png
nodes of two borders will be either merged or inserted into faces of
the opposite border.
+In practice the borders to sew often coincide and in this case it is
+difficult to specify the first and the last nodes of a border since
+they coincide with the first and the last nodes of the other
+border. To cope with this,
+\ref merging_nodes_page "merge" coincident nodes into one
+beforehand. Two figures below illustrate this approach.
+\image html sew_using_merge.png "Merge coincident nodes which are difficult to distinguish"
+<br>
+\image html sew_after_merge.png "After merging nodes it is easy to specify border nodes"
+
The sewing algorithm is as follows:
<ol>
<li>The parameter (U) of each node within a border is computed. So
