Inproceedings,

Lombardi Drawings of Knots and Links

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Proceedings of the 25th International Symposium on Graph Drawing and Network Visualization (GD'17), volume 10692 of Lecture Notes in Computer Science, page 113--126. Springer, (September 2017)
DOI: 10.1007/978-3-319-73915-1_10

Abstract

Knot and link diagrams are projections of one or more 3-dimensional simple closed curves into $R^2$, such that no more than two points project to the same point in $R^2$. These diagrams are drawings of 4-regular plane multigraphs. Knots are typically smooth curves in $R^3$, so their projections should be smooth curves in $R^2$ with good continuity and large crossing angles: exactly the properties of Lombardi graph drawings (defined by circular-arc edges and perfect angular resolution). We show that several knots do not allow Lombardi drawings. On the other hand, we identify a large class of 4-regular plane multigraphs that do have Lombardi drawings. We then study two relaxations of Lombardi drawings and show that every knot admits a plane 2-Lombardi drawing (where edges are composed of two circular arcs). Further, every knot is near-Lombardi, that is, it can be drawn as Lombardi drawing when relaxing the angular resolution requirement by an arbitrary small angular offset $\epsilon$, while maintaining a $180^\circ$ angle between opposite edges.

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