# Integration of BIM and GIS for the Digitization of the Built Environment
## 4 Results and Discussion  
The BIM-GIS integration presents a number of challenges, including those related to spatial scale, granularity level, geometric representation methods, archiving and access methods, and semantic discrepancies between the two systems. One of the principal challenges identified in the literature is the significant divergence in the information and data structures between standards developed with originally disparate purposes. It is evident that the integration of BIM methodology with data from thematic GIS maps becomes crucial to address the progressive loss of essential information and data in engineering, architecture and construction. BIM, on the other hand, is focused on infrastructure development and management, with a strong emphasis on object relationships. In contrast, GIS models the current geospatial context, where georeferencing plays a crucial role. Another significant challenge concerns the representation of geometric data, with different approaches between BIM and GIS. While BIM offers several methodologies for the three-dimensional representation of geometry, including CSG, B-rep and sweep, GIS primarily relies on the B-rep approach, with boundaries derived from straight lines and flat surfaces. The two-way transformation between the two standards remains problematic, particularly when converting from B-rep to sweep or CSG. Furthermore, the level of detail (LOD) definition differs between BIM and GIS, necessitating accurate mapping for proper conversion:  
* In the GIS environment, the concept of LOD in a tiling scheme defines the value of the zoom level for a map or scene view. This scale ranges from 0 to 23, with lower values indicating views further from the Earth and higher values indicating closer, more detailed views. A higher zoom level corresponds to more detailed geographic information, and a conversion tool is available to convert zoom levels to map scales, representing the relationship between map measurements and real-world measurements. The default zoom levels vary, depending on the type of layer used (vector raster layers vs. image raster layers), with vector raster layers typically having zoom levels one level lower than map raster layers. Understanding and correctly applying zoom levels and scales is essential for the accurate display of geographic information, increasing the precision and detail of map views for effective geospatial analysis and visualization. * In the BIM environment, LOD definitions act as the user's parameter set, to ensure that all parties involved in the BIM process build the model with a consistent level of content definition throughout all phases of the project design and execution. BIM processes can be categorized based on the level of detail of the information contained within the model, known as LOD. The American Institute of Architects (AIA) has established guidelines for levels of detail in the AIA G202-2013 BIM Protocol [81]. Recognizing that an element may appear visually detailed, but in reality remain generic, the term LOD refers to the \"level of development\" of model elements rather than their \"level of detail\". According to American standards, the level of development is divided into five distinct levels, from LOD 100 (Symbolic Representation), which is the elementary level of the project, represented graphically by a symbol or other generic schematic representation, to LOD 500 (As-Built), where elements are field-verified representations in terms of size, shape, location, quantity and orientation. Definitive non-graphic information is associated with geometric elements. These standards ensure a common understanding and consistency in the level of detail required at each stage of the BIM process, facilitating effective communication and collaboration among all project stakeholders. It is known that the discrepancies in LOD scales between BIM and GIS can be attributed to the intrinsic characteristics of the file format.