Many thanks for the hint, Bill!

I found that sample too. However, it is very difficult to create watertight closures with this approach. See what my result looks like. From distance things look okayish. However, if I zoom in, the result does not look good. What can I do to improve?

(Here a sketch of my implementation: <a href="https://pastebin.com/kPR1wKv6" target="_top" rel="nofollow" link="external">https://pastebin.com/kPR1wKv6</a>)

<img src="http://vtk.1045678.n5.nabble.com/file/t341102/Screen_Shot_2018-03-06_at_01.png" border="0" class="center"/>

<img src="http://vtk.1045678.n5.nabble.com/file/t341102/Screen_Shot_2018-03-06_at_01.png" border="0" class="center"/>

        
        
        
<br/><hr align="left" width="300" />
Sent from the <a href="http://vtk.1045678.n5.nabble.com/VTK-Users-f1224199.html">VTK - Users mailing list archive</a> at Nabble.com.<br/>