Abstract
Abstract. Mobile mapping systems are increasingly developing ad hoc solution and integrated approaches for rapid and accurate 3D digitization in different operating environments belonging to built heritage assets. The use of emerging compact, portable and low-cost solution for imaging and ranging well fits in the purposes of mapping complex indoor spaces especially for narrow and underground ones (tunnels, mines, caves and ancient spaces), that are very challenging contexts in which to experiment integrated technological solutions and tailored workflows. In these cases, the main key issues are generally the difficulty in the seamless positioning and the complete and successful metric-radiometric content association in metric surface, due to the reduced manoeuvring space and complex lighting conditions. The prevalent goals for which the 3D digitization could be conceived are, beyond the accurate metric documentation, the analysis of mutual relations of volumes in complex structures, the virtual reconstruction and navigation of spaces with reduced accessibility for dissemination aims. The new SLAM-based positioning solutions implemented in some recent portable systems for indoor/outdoor mapping are increasingly developing and favoured by geometric features extraction algorithms even in traveling through complex and irregular environments. In parallel, the possibility to exploit the advances in digital photogrammetry algorithms for image matching and dense reconstruction using action-cam, compact and fisheye cameras allows to deploy investigation solutions even in complex environments at first sight impossible to map by photogrammetric approach. Here within the F.I.N.E. benchmark in the site of the San Vigilio Castle (Bergamo) and the “nottole” tunnels, a fusion-based workflow is proposed. It is focused on the purposes of providing radiometrically enriched 3D data from the possibility to colourized ZEB point cloud and a textured mesh surfaces with an oriented image block, taking care of the time processing steps optimization.
Highlights
The research connected with MMS (Mobile Mapping Systems) have faced several challenges and transformations, especially in the fields connected with the survey of built heritage assets
In case of multi-sensors platform developed with single camera equipment (e.g. Zeb REVO by GeoSLAM) the process of radiometric data association is under development and the final product is still lacking a complete and high-definition RGB data
Some specificity of the Zeb point clouds are the added data that could enrich the point cloud geometry as: the SLAM-condition information, the time attribute, the geometry curvature value
Summary
The research connected with MMS (Mobile Mapping Systems) have faced several challenges and transformations, especially in the fields connected with the survey of built heritage assets. In case of multi-sensors platform developed with single camera equipment (e.g. Zeb REVO by GeoSLAM) the process of radiometric data association is under development and the final product is still lacking a complete and high-definition RGB data It would require a separated photogrammetric acquisition with high resolution sensor that led to a data integration or more, as in the proposed approach, to a fusionbased data processing experimental method. The reference ground-truth for the accuracy control of the proposed 3D reconstruction, in underground as well as in the tower floors, is a Leica RTC LiDAR (Light Detection And Ranging) points cloud Another range-based data was collected both in the tower and in the tunnel by means of a SLAM-based MMS, the. Some specificity of the Zeb point clouds are the added data that could enrich the point cloud geometry as: the SLAM-condition information (i.e. if SLAM profiles positioning works well according to the space conditions), the time attribute (i.e. the time progression of the measured profiles related to the trajectory), the geometry curvature value (i.e. the local orientation of the normal vectors of the point cloud)
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