Terrestial laser scanning digitalization in underground constructions

Abstract Spain has a large heritage in vernacular architecture among which the underground constructions can be highlighted. On many occasions these constructions were excavated hundreds of years ago and there is lack of technical information about their geometry or visual characteristics. Among the existing survey techniques, the terrestrial laser scanning technology seems one of the most appropriate and effective for these constructions. Given the high underground heritage in Spain and the lack of graphic documentation with good quality, there is a need to establish a quick and effective methodology aiming to classify these constructions in order to be included in the national heritage registers. To do so, the first step was to assess how aspects such as the scanner resolution, color and meshing strategy (post-processing phase) affect the quality of the graphic results generated. Then, the most adequate survey strategy was selected (based on a reference case study) and was further applied in seven representative underground constructions in order to validate the methodology and verify its effectiveness. Results indicate that a higher density of points is not always associated with a higher graphic quality in both the digital model and graphic information. The type of mesh used in the post-processing stage affects insignificantly the meshing surface, the graphic quality and the processing time of the digital model. On the contrary, it helps to filter unnecessary points in the cloud and thus obtain less heavy digital models. The resolution strategy can considerably increase the processing time of the models, however a lower resolution strategy combined with a higher number of shots is recommended to improve the graphic quality of the results.