# A Unified Database Solution to Process BIM and GIS Data
## 2 Materials and Methods  
The basis of the described research was an in-depth analysis of the literature, an analysis of the available BIM and GIS technologies in the field of building modeling, an analysis of the BIM/GIS market, and an organized discussion on the authors' experiences related to implementation works carried out for many years. The new conceptual approach was then formulated, and technological experiments and practical tests were performed. As a result, conclusions were drawn, and final solutions were proposed. Since 2007, a growing number of published research activities on data integration and exchange between BIM and GIS have been observed. Examples from 2007 include the authors of [6; 7; 8]. In the beginning, most of the proposed solutions were based on data migration using IFC and CityGML standards (the first official version in 2008). In the following years, proposals and research results were presented (i.e., in [9; 10; 11; 12; 13; 14]). Attempts to unify data types in both systems were made [15] in an attempt to facilitate their cooperation, since the structure of data referring to the same class of objects in both models is incompatible. Meanwhile, there were efforts to use GIS 4D technology for construction design [16]. GIS models (e.g., CityGML) were also used to import BIM data from the models of buildings available in KML (Keyhole Markup Language) format [17]. An interesting classification of the method of integration of BIM and GIS into five types was presented in [18], the first three of which refer to the integration at the data level:  
1. Conversion of BIM data into GIS based on the conversion of the IFC model into the CityGML model. As a result, BIM and GIS data are stored in the CityGML model and managed from the level of GIS software. This solution is often used by authors and users of GIS systems who require detailed data concerning a building. This issue has been discussed in numerous papers (e.g., [10; 14; 19; 20; 21; 22; 23; 24; 25]). 2. Conversion of GIS data into BIM based on the conversion of the CityGML model into the IFC model. As a result, BIM and GIS data are stored according to the IFC model and managed from the level of BIM software. This solution is mostly used in cases when architects or people who manage a building using BIM software require data concerning the building's surroundings [17; 26]. 3. The unified data model. Solutions in this category concentrate on developing a separate unified model to combine BIM and GIS data for selected analyses and particular applications [15; 27; 28]. Moreover, the Unified Building Model was proposed to provide two-directional conversion of BIM-GIS data [29; 30; 31; 32]. The next two approaches to integrate BIM and GIS data are at the application level:
4. Integration of BIM and GIS at the level of the application server. Solutions in this category offer a new concept of approaching the integration of BIM and GIS by introducing new IT (Information Technology) tools and extending existing applications so that it is possible to jointly operate BIM and GIS data. This is usually realized through the GIS application server [11; 33; 34; 35; 36; 37; 38]. 5. Integration at the level of the client application. Solutions in this category depend on transformations of BIM and GIS data downloaded by independent client applications such as GIS or FM (Facility Management) [6; 7; 39]. This type of classification was analyzed from a slightly different, although generally similar, perspective in [40]. The authors proposed a division into three integration modes: \"BIM leads and GIS supports\", \"GIS leads and BIM supports\", and \"BIM and GIS are equally involved\". In recent years, more and more research has indicated interest in the use of combined BIM and GIS data (e.g., [41; 42; 43; 44]). An analysis of the literature shows that the issues of BIM and GIS integration are in the area of scientific interest for many research centers, and thus far, there is no single unified approach for solving the problem.