The V3D software can be freely downloaded from http://penglab.janelia.org/proj/v3d. Additional tutorial movies and test data sets are available at the same web site. The database of stereotyped neurite tracts is provided at http://penglab.janelia.org/proj/flybrainatlas/sdata1_flybrain_neuritetract_model.zip. The entire database can be conveniently visualized using the V3D software itself (Supplementary Video 10).