## 3 The Case Study  
### As-Designed Data  
As mentioned above, a free-form building called Haewoojae was used as a case study to measure the difference between the as-built and the as-designed data of the facility. Figure 1a shows the exterior view of Haewoojae. Since the facility was initially designed in 2007 with 2D AutoCad and Maya program, the 3D BIM information and the curvatures coordinates of the facade panels had not been available. The structure of the facility consists of steel millions and transoms. Figure 1b represents the configuration of the frames. The facade of the building is composed of galbariums, i.e., zinc-galvanized aluminum panels, with urethane coating. When constructing the facility, the contractor had formed the panels by cold bending in the field according to the facade configuration and welded them to the steel frames. Figure 1c presents construction activities including panel fabrication of the roof area in the facility. The information on the layout of the aluminum panels was not available because the layout of the panels had not been a design element of the facility and coated with urethane coating. Figure 1d demonstrates the curved panel lines that had been fabricated before being coated. Window frames were installed under the panels. As stated in the Research Method section, the RE process was implemented to get the as-designed facade panel data of the facility. Digital Project (DP), developed by Gehry Technology, was utilized to identify the as-designed facade panel configuration, i.e., the curvature types of the facade panels, such as planar, single-curved, and double-curved, and their locations and numbers. In promoting the RE modeling process of Haewoojae, the designer of the building was invited from an early stage of the modeling to get advice on his major design concerns with the facility and critics on the RE modeling process and architectural shapes from the modeling in order to extract the precise shape of the facility. In developing a 3D BIM model of the facility, Georgia Tech process to product modeling (GTPPM) was followed. The GTPPM is a formal process-centric product modeling method which enables capture of domain-specific information and work processes through process modeling [27; 28]. The following steps were implemented in the modeling: (1) set up baseline for panelization; (2) determine the standard width and height for creating panel joints; (3) create equally spaced lines; (4) establish the standard of expressing geometric forms; (5) clean up complex, geometric shapes and cross line; (6) measure curvature and x, y, z, r values; (7) consider subdivision of panels if needed; and (8) create panels. Figure 2 represents the step-by-step procedures promoted following GTPPM. Panelization of the curved facade of the facility was performed with rectangular and triangular panel shapes. The basic panel size used in the modeling was 0.8 m \(\times\) 0.6 m and smaller ones were applied depending on the curvature configuration. The use of 0.8 m \(\times\) 0.6 m size was appreciated from the Dongdaemoon Design Park (DDP) project built in Seoul, Korea, 2013 [7]. The DDP is a free-form building designed by [PERSON] and has become a signature building of Seoul. The surface of the building had been designed to be covered with 45,313 panels, of which the basic panel size was 1.2 m \(\times\) 1.6 m. Approximately 48% of the panels (21,753 panels) were double-curved 4 mm-thick aluminum panels with folded edge. The author considered that DDP is a good reference to follow for this study but the panel size of 1.2 m \(\times\) 1.6 m used in DDP is too big to apply to the case study. The panels of DDP were formed by a multipoint stretch-forming method, which is a hybrid method of traditional stretch bending and multipoint forming, a state-of-the-art technique for forming various curved sheet metal panels by controlling the height of multilayered small presses by means of a multi-post hydraulic press [7].