## 2 Materials and Methods
### Creation of a Fixed-Object Model  
The resulting navigation network is stored in Transmodel (v6) format. In Transmodel, information about transport services and infrastructure is linked. The services use scheduled stop points. For the planning and operation of the services, the physical nature of stop points is not important. However, it is important for passengers to know where the stop points are located and how to reach them. For this purpose, the Transmodel defines stop places as representations of fixed objects of infrastructure. Stop places can be used to store information about the navigation network in buildings, train stations, airports, or ports. Both stop points and stop places can represent the same location and are connected throughout the trip-planning data model. According to the Transmodel, a _PLACE_ entity is defined as a geographic location of any type that can be specified as the origin or destination of a trip. A _PLACE_ can have dimension 0 (a _POINT_), 1 (a road segment), or 2 (a _ZONE_). A place may contain information about its accessibility, available services, and other relevant data, such as geographic location, information about available equipment, access requirements, and internal navigation routes. Places may be related to each other, and the model provides ways to describe these connections. The complete reference network-topology data model is defined in Transmodel Part 2--Public Transport Network. The network-topology model is divided into submodels. The Network Description submodel (ND) describes elements intended for public transport operations, such as lines, routes, and stops. The submodel ND and the Tactical Planning Components Model are outside the scope of our work. The third submodel, the Fixed-Object (FO) Model, describes the fixed infrastructure and provides a detailed view of stops, including equipment, accessibility, and navigation through the places. We used the FO model for extraction of infrastructure data from IFC models.  
Figure 2: Relationships between spaces, walls, and openings (ex. door).  
The Fixed-Object Model can and should be connected to related objects from other submodels when available to make the most of Transmodel's functionality. The Fixed Object Model also consists of submodels. To store the navigation network extracted from IFC data, not all entities from FO are needed. IFC might also not provide enough information to fully feed the FO model. For our purposes, entities from the _SITE_ submodel and the _STOP PLACE_ submodel were used. The subset of classes used is represented in a schema describing the site (Figure 3).  
A building or other fixed structure is represented as _SITE_ with geographic location and possible access options. If a _SITE_ represents a place where passengers access public transportation, SITE is considered a _STOP PLACE_ (other options include parking lots, service points, or points of interest). The _SITE_ could be further subdivided into _SITE_ _COMPONENTS_, which could be rooms, quays, corridors, and other parts of buildings that are part of the stop space (_STOP PLACE COMPONENT_). _ENTRANCE_ is also a specialisation of _SITE COMPONENT_ and represents an entry point into a space. This is one way to encode possible horizontal movement.  
_SITE COMPONENTS_ could be combined into _LEVEL_(s). The _LEVEL_ organises a building vertically. Vertical motion paths are encoded by another specialisation of _SITE COMPONENT_, namely _EQUIPMENT PLACE_. This is a placeholder for several types of _EQUIPMENT_ (s), such as _ELEVATOR_, _RAMP_, _ESCALATOR_, or _STAIRCASE_.  
For complex sites consisting of multiple buildings serving different modes, such as combinations of train station and subway, stops can be organised in a hierarchy that nests other stop places.