As part of the VisImp effort to bring cutting-edge research methods to VTK, an algorithm from a recent research paper in information visualization was implemented in VTK. The paper, Divided Edge Bundling for Directional Network Data, was written by David Selassie, Brandon Heller, and Jeffrey Heer at Stanford University and was published at the 2011 IEEE InfoVis conference. In it, the authors describe a new technique for bundling edges in order to see higher-level structures in complex graphs. The work expands on previous work to bundle edges by enabling directional lanes which highlight the amount of traffic travelling in each direction instead of grouping all the edges together. The images below show a graph of airline routes in the U.S. both without bundling (top), with bundling (center), and with divided edge bundling (bottom), with each diagram computed and rendered using VTK. Links are colored to show directionality (blue at their source and red at their destination).
The algorithm is available in the new class vtkBoostDividedEdgeBundling in the current development version of VTK. To the especially curious, you can see an example of how to use the filter in the associated VTK test.