## 4 Discussion
### The Technical Field
To avoid data loss, both the design team and the developer's team should make regular copies while complying with data confidentiality requirements. A parametric model of a building built using BIM, apart from enabling the generation of drawings needed to file for applicable permits, choose a contractor and for actual construction, can also be used during a building's use along with previously entered data. To this end, non-graphical data should be saved, for instance in COBie format (Construction Operations Building Information Exchange, example presented in Figure 2), which can be used throughout a building's entire life cycle. The necessity to save non-graphical data in COBie format in a SpreadsheetML version, which can be used by MS Office software, was mentioned in the EIR for the LPSC and KMC. The guidelines also included required training in software necessary for project execution that the design firm should provide for a group from the developer's team specified in the EIR. The EIR also specified the preferred metric units, coordinates (for the LPSC and KMC, the indications were PUWG PL2000 zone 7, PPK PL-2000, zone 6 and coordinates based on the EUREF-89 reference system), and the necessity to define a base reference point by the design firm. Another essential document in carrying out a construction project using BIM is the BIM Execution Plan (BEP), which is a detailed plan approved by the developer that extends an EIR's guidelines. The BEP is prepared by the contractor (in the cases analyzed these were design firms) and should be accepted by the developer prior to contract signature, as it is to be an appendix to the contract. This is how it functioned in the projects under study. Defining the level of detail (LOD) for geometric data and the Level of Information (LOI) for non-geometric data is an important component of an EIR's technical field. These levels depend on the project stage, i.e., whether it is conceptual, technical or a detailed handover design. The developer, by specifying in the EIR the expected, even general level of detail, minimizes the possibility of disappointment with the precision of the finished design. The designer, in agreement with the developer, has a greater motivation to introduce revisions  
Figure 2: Example of COBie sheet. Source: [48]. and analyze alternatives at a stage with a low level of detail, as there are less data to modify [49]. Definitions and specific levels of detail for model elements differ depending on guidelines. For instance, British guidelines featured in the PAS-1192-2-2013 [50]_Level of Definition_ were divided into those that concern the Level of Detail (LOD) for geometric data and the Level of Information (LOI) for non-geometric data, with a seven-grade scale from 1 to 7. A document published by BIMForum also introduced the Level of Development (LOD [51], which is described as a broader term than Level of Detail, but that does not divide the scale into geometric and non-geometric data. The Level of Development consists of a six-level scale, from 100 to 500, with level 350 applying to the joints between elements, supports and level 500 referencing only non-geometric data (field verification). The ISO 19650 standard [37] introduced the broad Level of Information Need. In Polish standard proposals compliant with the PN-EN ISO 19650 standard [52], a five-level scale of 1 to 5 was proposed, describing levels for the following categories: Level of Graphical Detail (LOgD), the Level of Model Information (LOmI), coordination (application in 3D), work schedule (implemented in 4D), bills of quantities and costs (implemented in 5D) and facility management (implemented in 6D) [47]. For road engineering projects, a five-level division was proposed, from 1 to 5, similarly to the British guidelines, with a division into geometric and non-geometric data, based on the example of bridge construction [53]. There is also another Polish proposal [54], yet it is too general in terms of levels of detail/development or references other standards.