## 5 Conclusions  
At present, the realization phase of railway constructions ends with the preparation of 3D CAD as-built documentation, which is used for its subsequent operation and maintenance. The transformation into a common BIM or GIS data environment is intended to streamline the use of this documentation in the operational phase of the construction, while the BIM model is to be used effectively for e.g., maintenance planning. In the paper, the method of transformation of data obtained from the as-built state survey into the BIM and GIS environment was presented. The proposed solution was verified on a case study of the realized project of the railway station Sumice (Czech Republic). The BIM data standard created by the State Fund of Transport Infrastructure was used for the documentation remodelling. The research published so far has mainly dealt with the transformation of data from CAD to BIM or GIS, i.e., from a discrete space (CAD) to another discrete space (BIM, GIS)--see e.g., [4; 59]. The contribution of the proposed method is the transformation from the real space of the construction to the discrete space of CAD (as-built documentation) and then to BIM and GIS. The conversion identified the following main issues:  
* conversion of features and attributes from CAD to BIM/GIS,
* differences in geometric accuracy between source and target graphics of these platforms. The authors propose an acceptable solution within existing CAD/BIM/GIS applications. It is shown that current software systems are not yet able to capture geometric shapes in real space with 100% accuracy. This fact was confirmed by the results in [65]. Further inaccuracies may result from the exchange formats used, as confirmed by the experience of [57]. BIM documentation is particularly effective when the entire construction process is managed in BIM mode from the start. For existing buildings that have not been managed in BIM from the start, the as-built documentation needs to be reworked into a common BIM data environment. The conversion of existing conventional construction documents into BIM is very time and cost consuming, mainly due to the differences in data structures. From the current state of the RA standard [60] and the BIM standard [6], it has been analyzed that the remodelling of classical 3D CAD documentation into a BIM CDE can be realized automatically from 65%, the rest of the data content is necessary, i.e., 35%, requires the necessity of individual human decision making during the remodeling. This fact is due to the lack of pan-European standards for describing the railway network at the level of the interchange format (e.g., IFC). Therefore, so far non-standardized processes are the subject of research activities not only in the Czech Republic [52; 55]. A significant benefit of reworking the original CAD documentation into BIM is the streamlining of approval processes during the preparation and execution of constructions. The most detailed data is generated in the construction realization processes administered in BIM, which then serves as a source of data for passport-type agendas, into which they are taken automated by engineering processes. Another benefit is the streamlining of data updating of internal systems of the Railway Infrastructure Administration, e.g., Digital Technical Map of Railways, Technical Passportof Infrastructure and the possibility of data sharing to downstream systems of the state administration (DTM CZ) in accordance with INSPIRE. The research will continue with the design of a suitable data model that would eliminate these data conversion problems between CAD/BIM/GIS platforms to the maximum extent possible. The main contribution of the research is the inter-convertibility of data between the completely different data models specified by the Railway Administration standards and the newly emerging BIM standards.