The Path Fitter is a maximum likelihood fitter which uses different calculated PDFs for each electron position, direction, and time in the detector. Each calculated PDF contains both PMT timing and angular information that is used in fitting. The Path Fitter also provides several goodness-of-fit tests which can be useful for rejecting bad fits as well as non-Cerenkov events in a data sample.
More information can be found in SNO-STR-2000-022, ``Using Time and Angle Information in Reconstruction and the SNOMAN Path Fitter.'' (work in progress) and the command file run_path_fitter.dat.