## 2 Methodology  
Figure 3 shows the proposed methodology for the 3D simulation of building facilities maintenance management. This process consists of creating digital GIS and BIM models (PHASE 1); integrating and enriching them with accurate information (PHASE 2); and, finally, applying the integrated model to simulate 3D maintenance management of the building's facilities (PHASE 3). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Software** & **REVIT** & **AUTOCAD** & **ARCHICAD** & **TEXLA** & **NAVISWORKS** & **SketCHUP** & **RHNOCGROS** & **BENTLEY** \\
**CMMS** & & & & & & & & \\ \hline _YouBIM_* & ✓ & ✓ & ✓ & ✓ & & & ✓ & \\ \hline _Revizto_** & ✓ & ✓ & ✓ & & ✓ & ✓ & ✓ & \\ \hline _EcoDomus_*** & ✓ & & & ✓ & & & ✓ \\ \hline \hline \end{tabular}  
* Allows the integration of pdf documents. ** Allows the integration of point clouds and pdf documents. *** Allows the integration of point clouds.  
\end{table} 
Table 1: Interoperability of CMMS software with other 3D BIM software. Author’s elaboration based on [18]. Figure 2: Systems (in text) and subsystems (symbols) of the building. PHASE 1, _Modeling_, is divided into two stages, one consisting of the creation of the GIS-3D environment of the site and the other of the creation of the BIM models of the buildings. For stage 1, _Creation of the site GIS-3D environment_, a three-step methodology is proposed. In step 1, _Data management and initial configuration_, the first action to be taken is to define the semantic level (level of detail and type of terrain) that the GIS-3D model will have. The initial data for building the model include the base map, which will serve as the GIS platform; the LiDAR (light detection and ranging) point cloud data of the geographic area; and the cadastral base of city plots, a two-dimensional GIS layer containing a table of municipal and cadastral attributes. In step 2, _Definition of the Terrain and the Footprint of the Buildings_, the focus is on using the cadastral base of city parcels to extract \"building footprints\" needed for the 3D model. These footprints are represented as 2D polygons linked to a database containing municipal and cadastral data, including building level specifications. If terrain relief is to be incorporated, the digital terrain model (DTM) and digital surface model (DSM) are created from LiDAR point cloud data to ensure modeling accuracy in later steps. In step 3, _Generation of the GIS-3D Environment of Buildings_, the 3D  
Figure 3: Schematic representation of the three phases of the proposed methodology for simulating 3D building facilities maintenance management. building model is developed within the GIS platform, with levels of detail (LoDs) ranging from LoD 1 to LoD 4, depending on the project specifications. For LoD 1, the model uses building footprints and associated attributes from step 2. For this purpose, algorithms can be employed to extrude the building footprints from the digital height model (DHM) or to assign a standard height for each building level. For more detailed models (LoD 2 to LoD 4), raster-based tools are recommended. In PHASE 1, stage 2, _Creation of the BIM models of the building_, the proposed methodology includes two steps (Figure 3): step 1, _Preliminary information and data capture_, and step 2, _Creation of the geometric model_. In step 1, existing building data are collected to create and populate the BIM model in the following step, drawing on sources like sketches, measurements, plans, large-scale position capture (LiDAR point clouds), technical data sheets, or family libraries, among others. Step 2 involves virtually constructing the building in BIM software, requiring both 3D modeling skills and technical building knowledge. The goal is not merely to create a geometric representation but to form a BIM model with parametric intelligence, providing both quantitative and qualitative data. The focus should be on using BIM as a knowledge tool rather than on achieving precise 3D detail [25, 26].