Efficient Solutions for the 3D Survey of Narrow Spaces: The Case Study of the Bell Tower of the S.S. Trinita Church in Popoli (Italy)

Surveying narrow spaces in 3D can be challenging due to limited accessibility, safety concerns, and the need for precise data. The paper aims to identify solutions based on passive and active sensor-based techniques and algorithms to build the 3D model of narrow space, such as the internal bell tower. However, to reconstruct the 3D model of the entire bell tower, it is necessary to survey both the exterior and interior parts. While for the exterior of the tower can be used the UAV photogrammetry, for the survey of the interior, it is necessary to find solutions that can ensure continuous and accurate patterning in confined environments with poor lighting and logistical difficulties in placing instruments on tripods. A solution was identified in the use of Simultaneous localization and mapping-SLAM, which allowed the 3D model of the belt of the S. Trinità church in Popoli (Italy). However, in order to find an excellent reconstruction, it was necessary to calibrate an appropriate path. In this way, it was possible to ob tain an accurate and detailed numerical model that could reconstruct the geometry and texture of narrow and dark environments. To highlight the potential of this approach, a survey with spherical cameras and photogrammetric processing was also performed; in the latter case, limitations were found in the geometric and density reconstruction of the point cloud when compared with the SLAM survey.