## 2 State-of-the-Art of Systems for Indoor Mobile Mapping (iMMS)  
The increasing demand for three-dimensional surveys to extract BIM models of existing buildings has been accompanied by the increasingly widespread use of terrestrial laser scanners (TLSs) [15, 16, 17, 18, 19, 20, 21]. In all those cases where restoration or renovation of an existing building is to be carried out, if the project is to be realized with a BIM approach, it is necessary to do a three-dimensional survey and then an extraction from the point cloud model of a parametric model. The laser scanner survey operation and subsequent modeling of pipes, pipelines, and tanks have rapidly become standard in industrial settings, particularly in oil and gas facilities, where the operation, known as \"scan to BIM\", has found rapid application and success [22, 23]. The regular and standard geometries of the service networks of these facilities have rapidly demonstrated the high effectiveness and productivity of automatic or semi-automatic geometry recognition, in particular in oil and gas environments using point clouds acquired by static laser scanners [17, 23, 24, 25]. In contrast, in the fields of construction and real estate, these tools are significantly less effective. Consequently, the modeling operations, specifically the scan-to-BIM process, are primarily based on the operator's manual actions, resulting in significant costs and time. Nevertheless, operational issues remain to be resolved and effectively managed, such as using artificial intelligence algorithms. The scan to BIM in real estate and construction is primarily based on the creation of catalogs of known geometries, which the operator has to recognize and apply to the point cloud model of reality, rather than on processes that allow the automatic extraction of geometries from the point cloud [26, 27]. The scan-to-BIM process is challenging for many projects with restricted budgets. Because of this challenge, the laser scanner is frequently employed in surveying applications on existing buildings, resulting in the production of 2D representations of floor plans and elevations. The point cloud is used just to extract point cloud profiles, and the restitution of the floor plans, profiles, sections, and elevations to CAD is performed manually by operators. Consequently, the BIM model is generated by starting from the floor plans and manually adding the heights measured by the laser scanner model into the modeling software. Further difficulties that have limited the laser scanner's widespread adoption are attributable to the fact that to merge the three-dimensional scans obtained from various stationing positions with the laser scanner, each scan must observe at least three targets that are common to the adjacent scans. The processing times required to obtain the complete point cloud model, in the case of buildings with a regular structure such as those described in this article, are nevertheless lengthy, with an estimated duration of approximately three times the time required to scan the point cloud in the field. The processing time can be much longer in the case of more complex buildings, as stated by [PERSON] [13] \"the amount of energy and time to create an accurate and faultless model is many times larger than scanning time (roughly by factor 5 to 10 or even more)\". Initially, this issue was one of the main challenges that data-processing software developers and TLS instrument manufacturers attempted to speed up the alignment processes between scans. The operation of locating and recognizing targets or markers used to align adjacent scans, as well as the on-the-field displacement of printed targets or spheres, are time-consuming procedures. On the other hand, the effectiveness of automatic alignment algorithms might not produce accurate and stable results [28; 29; 30; 31; 32]. For this reason, the utilization of targets for align scans is still prevalent in outstanding applications, as it ensures the quality and accuracy of the registration process.