This paper presents new methods of 3D visualization of graphs that allow to highlight nodes structural centrality. These methods consist in projecting, along the vertical axis, 2D graph representations on three 3D surfaces: 1) a half-sphere; 2) a cone and 3) a torus portion. The transition to 3D allows to better handle the visualization of complex and large data that 2D techniques are generally unable to provide. The 3D radial layout techniques reduce nodes and edges overlap and improve, in some cases, the perception of nodes connectivity by exploiting differently or better the display space.

In this paper we propose improvements to the 3D radial layouts that make it possible to visualize centrality mea- sures of the nodes in a graph. Our improvements mainly relate edge drawing and the evaluation of the 3D radial layouts. First, we projected not only the nodes but also the edges onto the visualization surfaces in order to reduce the node overlap that could be observed in previous 3D radial layouts. Secondly, we proposed a human-centered evaluation in order to compare the efficiency score and the time to complete tasks of the 3D radial layouts to those of the 2D radial layouts. The evaluation tasks proposed are related to the central nodes, the peripheral nodes and the dense areas of a graph. The results showed that 3D layouts can perform significantly better than 2D layouts in terms of efficiency when tasks are related to the central and peripheral nodes, while the difference in time is not statistically significant between these various layouts. Additionally, we found that the participants preferred interacting with 3D layouts over 2D layouts.