Gaetano Impoco Paolo Cignoni Roberto Scopigno Closing Gaps by Clustering Unseen Directions (Figures 5, 6, 7, and 8). 397 2004 conf/smi/2004 SMI https://doi.ieeecomputersociety.org/10.1109/SMI.2004.10004 db/conf/smi/smi2004.html#ImpocoCS04a