Hi Johan,
I've just commited RTAnchorConstraint to latest Roassal, see class-side example there.
I've been using it for my class diagrams where it works quite well, however class diagrams are usually orthogonal-ish, which makes it a bit nicer.
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The Anchor will avoid intersecting it's own line, and one of the end shapes (it should both but apparently I have a bug there...).
It doesn't look at other lines, however you can specify on which side it should be.
(You can also put the node label inside the circle with ��`el @ (RTLabelled new center)` but you probably know that.)

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I have also a global edge labeling layout which produces good placement��� but it's slow as hell��� I need to write a fast flow alogrithm���
Also the Anchor currently doesn't work with self-edges. On the other hand Roassal doesn't have self-edges yet so it shouldn't be a problem. :)
Peter