5.2 Reconfigurable Disc Trees

Chang Sung Jeong ( Korea University , mailto:csjeong@charlie.korea.ac.kr), Alex Pang (UC Santa Cruz, http://www.cse.ucsc.edu/~pang)

“Reconfigurable Disc Trees for Visualizing Large Hierarchical Information Spaces” presented an interesting enhancement of the now classic “cone tree” method for hierarchy visualization. A cone tree creates a circle of nodes for each level of a hierarchy and connects them in a cone shape with the apex at the next higher level. Cone trees have three main drawbacks:

1. it is hard to prevent occlusion by cones in the foreground
2. the number of nodes that can be displayed is very limited
3. visual clutter is unavoidable when the tree is projected on a planar surface (shadow)

The key aspect of the Reconfigurable Disc Tree (RDT) is the introduction of two control nodes for each cone: the reference point and the apex point. The reference point is a node above the center point on the plane of the parent node. The apex node is the top of the cone. Different tree shapes are created by changing the distance between the parent node, reference point, apex node and center point of a cone base. The reference point can be offset from the parent node, broadening the tree. The cone can be flattened into a disc by making the apex == center point.

The paper presented algorithms for various layouts and evaluations of them. The conclusion was that RDTs can provide significantly better displays than standard cone trees. Given that cone trees are a subset of RDTs and the flexibility of RDTs, a visualization system would do well to implement RDTs instead of simple cone trees.

One application of RDTs in the paper is a collaborative Command and Control system. Role specific and common RDTs were used to visualize task and organization hierarchies.