The validation process of a 3D multisource/multiresolution model for railway infrastructures

The technological evolution that marks the passage from traditional cartographies towards topographic databases in term of Spatial Data Infrastructures (SDI) is characterised, at the surveying level, by the availability of different sources and tools for acquiring data: remote sensing, drones, laser scanners, etc. These multi-diversity sources have a significant impact during the dataset evaluation phases: above all, for each individual step, a specific sensor is used and its technical characteristics are taken into account, as well as the connections between the different steps that contribute to create the final database. Therefore, data product specification is the first step towards understanding which spatial database quality and requirements must be satisfied. At this transitional time, while the sources and tools have yet to be established in the processing and methodologies, this article will try to focus on critical issues encountered during a validation process of a geographical infrastructure in the railway context. The validation process has been carried out by a step-by-step approach. Basically, a consolidated validation methodology has been adopted for traditional products also carried out by new sensors, while a comparison with ISO (International Standard Organization) standard specifications has been followed for innovative survey (Mobile Mapping Systems (MMS)). Finally, for the GeoTopographic DataBase (GTDB) both massive (informatics procedures) and traditional thematic evaluation of accuracy have been combined. Therefore, the adherence with standards has been referred to take into account both the quality of data and the conformity to data product specifications. The considerable variety and the amount of the provided data, the harmonisation between different evaluation processes, the need to validate with short time and the lack of on-the-field surveys have been hardly considered as requirements, as well as the compliance with standards together with traditional cartography evaluating approaches.