## 3 The Case Study
### As-Built Data  
Three-dimensional laser scanning technology was used to obtain the as-built data of Haewoojae. Among a number of laser scanners in the market, the study utilized Leica Scanstation C-10 time-of-flight (TOF) scanner from Leica Geosystems [29]. There are two common operating principles for laser scanning, i.e., TOF and phase comparison [30]. TOF laser scanning computes the coordinates of its surroundings on the basis of the amount of time a single laser signal takes to return to the scanner after being echoed. This process takes place a great number of times until the given range of data assembly is achieved. On the contrary, the phase comparison method conveys a laser beam which is modified by a harmonic wave. When the modulated beam comes back to the scanner, the phase difference between what was conveyed and what was returned contributes to the calculation of distance.  
Scan accuracy is an important consideration when using the data from a laser scanner. In scanning an object, a large number of 3D coordinates on the object's surface is measured in a very short time. Although it is possible to record the object a number of times from different observation points, it is impossible to record the very same points in these repeated observations. Deviations, in consequence, can be noticed after the object has been extracted from the point clouds resulting from laser scanning and modeled. If the geometric properties of the object are known, the deviation of certain points from the object's surface can be an indication of scan accuracy [29].  
A number of specifications from laser scanner vendors claim that current laser scanning devices provide at an accuracy with a standard deviation of a few millimeters. According to the technical specification for the Leica C-10, the accuracy of the scanned data referred to one sigma is \"uncertainty \(\pm\)4 mm, 50 m range.\" Rather than performing an accuracy test for the scanned data of Haewoojae, the study referred to the accuracy indication of the specification since the scanning distance was roughly within 30 m, as shown in Figure 4a.  
Figure 4: Laser scanning locations around Haewoojae.  
Figure 3: Locations of the different panel types in Haewoojae.  
The volume scanned was approximately 2900 m\({}^{3}\) over two stories and 418 m\({}^{2}\) of gross floor area of Haewoojae. The initial step of laser scanning was to set up scan points. Figure 4b presents six scan points established to get the point cloud data of the facility, i.e., five points around the facility and one on the roof. The points were arranged to secure enough overlap of scanned areas thereby obtaining a confident shape of the facility. Bright green lines around the center of the five red circles indicated the boundary of the facility scanned. The scanned data were then refined removing unnecessary noise in each scanned area and merged together. The merging process was performed following the overlapped location and shapes in each of the six scanned areas. Based on the merged shape, the building outline and surface were made as shown in Figure 5a.  
In general, to model surfaces of scanned facilities, commercial software such as Maya, Rapidform, Geomagic, and Polyworks has been used in the past [6]. However, these applications generate a simple polygon CAD file without delivering the parametric volume elements of scanned objects through automatic conversion of data. Just as the as-designed data of Haewoojae was obtained with DP, the study utilized DP again to produce the surface outlines of the scanned facility data and converted those to BIM parametric data for comparison. Figure 5c shows the final surface model of the facility based on the data from laser scanning.