A new automatic method for discontinuity traces mapping and sampling on a rock mass digital model is described in this work. The implemented procedure allows one to automatically identify discontinuity traces on a Digital Surface Model: traces are detected directly as surface breaklines, by means of maximum and minimum principal curvature values of the vertices that constitute the model surface. Color influence and user errors, that usually characterize the trace mapping on images, are eliminated. Also trace sampling procedures based on circular windows and circular scanlines have been implemented: they are used to infer trace data and to calculate values of mean trace length, expected discontinuity diameter and intensity of rock discontinuities. The method is tested on a case study: results obtained applying the automatic procedure on the DSM of a rock face are compared to those obtained performing a manual sampling on the orthophotograph of the same rock face. ► A new method for discontinuity traces mapping and sampling on a rock mass model. ► Automatic identification of discontinuity traces to estimate degree of fracturing. ► Quantitative evaluation of rock mass quality based on photogrammetry/laser scanner. ► Method to quickly analyze huge amount of trace data. ► This is part of a research ongoing at University of Parma from 10 years.