# Analyzing the Economic Performance of a TLS-Based Structural Safety Diagnosis Process
## 2 Materials and Methods
### TLS-Based 3D Scanning Reverse Modeling Process  
In the construction industry, digitalization is progressing along several axes, including 4D/5D BIM [36; 37], RFID [38], and the use of drones/robots [39]. Two technologies that have gained particular attention in the field of structural safety inspection are TLS and BIM [3; 35].  
TLS is a technology that uses a laser scanner to acquire three-dimensional point cloud data of the surrounding environment or facility. By rotating the scanner in the field, it emits and receives lasers to accumulate a large number of coordinate values of the corresponding points [40; 41; 42]. In the process, high-precision, high-resolution data can be obtained quickly, which can significantly reduce the manpower and time required for the safety diagnosis of large-scale facilities that would otherwise be time-consuming if assessed using visual inspection [43]. TLS has been applied in a variety of fields, including displacement monitoring of large structures, such as underground structures and tunnels [44], bridges [8], and older buildings [3], and for as-built modeling [8; 10] and quality inspection [45]. In particular, [PERSON] and [PERSON] [3] reported a case of utilizing scanners on an old building, which resulted in a 4-month construction period reduction, 125 man-hours saved, and 50% cost savings compared to traditional construction methods. However, technical and economic barriers exist, including equipment price, field-of-view issues when scanning in the field, and the need for noise removal and data post-processing [46; 47]. In addition, the availability of software and experts to manage and analyze large-scale point cloud data is also an essential factor to consider.  
BIM is a system that manages the physical and functional information of a facility as a digital model. BIM provides a digital platform to support decision making throughout the entire life cycle of a building, including its design, construction, operation, maintenance, and demolition [48; 49; 50; 51]. When 3D point cloud data scanned with TLS are linked to a BIM platform, it is possible to quantitatively compare displacements or damage conditionsand to automatically calculate repair and reinforcement quantities [52; 53]. By comparing aging steel structures with BIM models, corrosion areas, deformed spans, etc., can be visually identified, which improves the speed and accuracy compared to traditional 2D drawing-based methods [13; 54]. However, the initial investment is high, including the acquisition of BIM experts, software license costs, and the additional workload required to transition from traditional 2D drawings to 3D models [55; 56]. In addition, it is also pointed out that BIM data compatibility is poor due to the different work standards across sites and companies [55].  
Although the combination of TLS and BIM can be expected to have strong synergies in the structural safety diagnosis process, there is insufficient evidence to demonstrate the economic benefits in terms of investment costs in real projects [13; 57]. [PERSON] et al. [58] estimated the labor cost reduction effect of applying TLS in a building quality assessment, but the case study was limited to a single project, which limits the generalizability of the results. Therefore, it is necessary to verify the long-term ROI through multiple project cases, cumulative analysis at the company level, etc.