Human perception of graph drawings is influenced by a variety of impact factors for which quality measures are used as a proxy indicator. The investigation of these impact factors and their effects is important for evaluating and improving quality measures and drawing algorithms, as well as improving our understanding of human graph reading. The number of edge crossings in a 2D graph drawing has long been a main quality measure for drawing evaluation. The use of stereoscopic 3D graph visualisations has gained traction over the last years, and results from several studies indicate that they can improve analysis efficiency for a range of analysis scenarios. While edge crossings can also occur in 3D, there are additional edge configurations in space that are not crossings but might be perceived as such from a specific viewpoint. Such configurations create crossings when projected on the corresponding 2D image plane and could impact readability similar to 2D crossings. In 3D drawings, the additional depth aspect and the subsequent impact factors of edge distance and relative edge direction in space might further influence the importance of those configurations for readability. As a main contribution, we for the first time discuss potential impact factors. We discuss hypotheses on their impact, and as an initial investigation explore the impact of three selected factors in an empirical study.

Human perception and understanding of graph drawings is influenced by a variety of impact factors for which quality measures such as the number of crossings are used as a proxy indicator. For the more and more common stereoscopic 3D (S3D) graph visualisations, evidence is required to better understand graph perception and its relation to quality measures. We investigate the perception of crossing configurations in S3D graph visualisations and present the results of a study.

Celtic knots, an ancient art form often linked to Celtic heritage, have been used historically in the decoration of monuments and manuscripts, often symbolizing the notions of eternity and interconnectedness. This paper introduces the framework CelticGraph designed for illustrating graphs in the style of Celtic knots and links. The process of creating these drawings raises interesting combinatorial concepts in the theory of circuits in planar graphs. Further, CelticGraph uses a novel algorithm to represent edges as Bézier curves, aiming to show each link as a smooth curve with limited curvature. We also show that with our production mechanisms we can compute any 4-regular plane graph and thereby any celtic knot or link. The CelticGraph framework for drawing graphs as celtic knots and links is implemented as an add-on of Vanted, a network visualization and analysis tool.