Identification and reconstruction of trajectories from the digitised output of a modern tracker can, in the simplest cases, in the absence of a magnetic field and absorbing/scattering material, be achieved via straight-line segment fits. A simple helical model, to determine momentum in the presence of a magnetic field, might be sufficient in less simple cases, through to a complete (e.g.) Kalman Filter process, to provide a detailed reconstructed local model throughout the complete track in the most complex cases.