Balloon layout

The Balloon layout places each node children in its enclosing circle (centered at the root node)using some optimized algorithms. The nodes are placed to avoid overlapping between nodes and to make the graph as compact as possible unlike the older balloon algorithms. Angular resolution and aspect ratio are optimized in this layout to provide clearer graphs and to optimize space occupation of the calculated embeddings.

The Balloon Layout takes as input the number of nodes of a given Graph and their connections to compute an internal structure based on the graph topology and the user preferences. In fact, if the graph is Tree and digraph, the unique root node and the correspondent internal structure are computed. However, if the graph is not a digraph, whether the graph is a tree or not, the layout algorithm automatically select the most weighted node, having the maximal number of links. Therefore, the layout is able to handle effectively any graph type (by ignoring cycles) using different root selection policies.

This Layout provides some extra options enabling more control on the geenrated graph representation :

• root selection policies (rootSelectionPolicy);
• nodes spacing (nodeSpacing): controlling the minimal spacing between nodes and therefore the compactness of the graph;
• angular resolution for root node (rootAngularSector) and child node (childAngularSector) : defining the angular sector in which nodes are laid.
• Enable Even Angles (useEvenAngles) : assigning equal angular sectors for all nodes' children (an old approach). By default set to false, the balloon layout algorithm optimize space filling via assigning different angular sectors (proprtional to the sub trees weight).

In Visualizer component, we have added collapse/expand capabilities to this layout. In fact, it is possible to collapse a node by hiding its children for a higher overview of your data, or you can expand a node in order to view its children to see your data in a more fine grained state.
You can define a visibility level so that you see only your data nodes up to a certain level of detail. This is very useful when it comes to see the relative performance of key indicators with the same depth in the hierarchy.

Like radial layout, the Balloon layout is suited to represent computer and social networks. It can be also used in some network analysis applications. Balloon layout is particularly used to browse and explore large hierarchies and non dense graphs.

Projects using this layout : Visualizer and Diagrammer