See http://cvgmt.sns.it/paper/3120/ for an explanation of what a bubble cluster is.
The file sandwich+cluster.ipynb is a iPython notebook. You can view the results of the computation by opening the file in the github repository: https://github.com/paolini/sandwich/blob/master/sandwich%2Bcluster.ipynb
To modify the notebook you either need to install jupyter on your computer or obtain access to a jupyter server. See http://jupyter.org/