3d Geo-information Indoors: Structuring for Evacuation

Interiors of buildings are often represented as two-dimensional spaces with attributes attached to them. Examples can be found everywhere, from architectural design plans to maps showing evacuation routes in emergency cases. Most of the navigation programs use primarily 2D plans for visualization and communication. Some exceptions are historical buildings and museums, which do offer navigation through textured, detailed 3D indoor models. However, these models are not structured with respect to the functionality of the building but largely with respect to the navigation/visualisation route. Structuring the interior is not a straight forward task, as many concurrent decompositions of a building have to be accommodated (e.g., functional, according to building structure, accessibility-wise), which are very dependent on the application. Furthermore the semantic/terminology is still not unified and in many cases ambiguous. A very typical example are inner open-air courts, which are open-air but inside the building. In this paper we present a semantic model of interior spaces. The structuring aims at facilitating calculation of evacuation routes and therefore particular building characteristics related to exit possibilities such as available doors and windows are considered as leading in the followed approach. The classification concept is used to build a graph for one of the buildings in the campus area. The geometry of the building and corresponding graph are organised in a geo-database management system (geo-DBMS) 3D models of interiors have been created predominantly for visualisation purposes to guide users in buildings of historical (cathedrals, castles), architectural, cultural (museum) or other (airports) importance. These models are mostly not structured except for visualisation and navigation purposes. Usually the structure is built to speed up visualisation/navigation process. In the last few years the attention in modelling interiors increases. Several tragic incidents have already suggested the current systems for evacuating people from large public and business buildings is not efficient (Cutter et al, 2003, Pu and Zlatanova, 2005). The research currently is on intelligent buildings systems to monitor and integrate data from a variety of sensors (temperature, movement or occupancy sensors, pressure pads, smoke or gas detectors, fire detectors) for detection, alarming and controlling other systems (heating, ventilation, air flow, lock/unlock doors, lighting, etc. (Reyes et al 2001). However, most of the existing systems are based on 2D environments, which reveal serious limitations when considering multi-level structures (Kwam and Lee, 2005, Zlatanova et al 2004). A building is represented as a combination of different types of spaces (rooms, compartments and different connection) but in 2D (Gillieron and Merminod, 2003). In this paper we report a semantic model representing 3D structuring of interiors to be used for an intelligent computation of evacuation routes. The model consist of two levels (polygon and section), which take into account the possibilities to move through buildings. A semantic classification of polygons with respect to different characteristics is introduced as the first level (i.e. polygon level). Sections are specified at the second level (i.e. section level) on the basis of the polygon classification. Particular polygons and sections are accordingly mapped to nodes and edges of graph, which is used for routes calculations. The model is implemented in geo-DBMS using spatial data types and network possibilities of Oracle Spatial 10g. The paper is organised in six sections. Section 2 presents the polygon and space partitioning. Section 3 discusses the process of graph creation. Section 4 gives a short overview on the network model of Oracle Spatial and presents the database implementation. Section 5 concentrates on the used data sets, implemented algorithms and the tests currently performed. Last section addresses future work and development. SEMANTIC MODEL FOR EVACUATION FROM BUILDINGS To be able to define meaningful routes to move within buildings, doors and other eventual exits, which can be used only in extreme cases, have to be explicitly modelled. Since the most common representation of these objects in 3D models is with polygons, we have use polygon as the smallest unit in our model. All the polygons in a building are given meaning with respect to their role in allowing people to walk around. Most of the polygons are just concrete walls and it is clear people cannot pass through them. However, there is a large variety of openings (with or without doors) that need elaborations. The polygon classification presented here is based on four properties: persistence, existence, access-granting and types of passing: 1. The persistency of polygons reflects the possibility of a polygon to be temporarily removed (if needed). A very typical example of non-persistent polygon is a wall that can be folded and thus two spaces can be joined. This property of a polygon is further organized as a status operation ‘being there’ and ‘not being there’. Figure 1: Persistent (door and wall, left ) and virtual (virtual polygon closing the kitchen, right) polygons 2. On the basis of existence two types of polygons can be distinguished (Figure 1): real (e.g. walls) and virtual (e.g. virtual walls do not exist in reality but only in the model to close sections). This classification is critical for visualization process; virtual polygons should not be rendered. 3. We introduce two groups of polygons considering the accessgranting. Non-granting polygons prohibit entering a section (e.g. wall). Granting polygons (Figure 2) allow three types of entering full (no conditions, these are the exits, e.g. polygons representing doors), semi (usually exists but have some restrictions, e.g. one needs to have a key) and limited (under normal circumstances not used as exist, e.g. emergency exist and windows). Figure 2: Granting polygons with full (door, left) and limited (window, left and exits, right) passing. 4. The types of passing can be uniand bi-directional depending on the possible way of entering. For example many exits allow only one-way of entering. The consequence of such an entrance is that once inside a particular section the person may not get out using the same way. Figure 3: Non-accessible sections (columns inside a room, left) and end section (right) The classification made for the section level is based on complete subdivision of space. The building is separated into relatively well-defined parts called sections. A section is defined as being the smallest amount of bounded space in a building that has a specific function (e.g. meeting room, stairs, etc.) with the following restrictions: • Sections must be closed. If not closed in reality, virtual polygons must be introduced. Examples of such ‘open’ spaces are stairs, corridors, elevators, etc. • Section must be distinct and may not overlap with any other section. We distinguish between three types of sections: end (only one entrance/exit, Figure 3, right), connector (more than one entrance/exit) and nonaccessible (no entrance/exit, Figure 3, left) sections. Connector sections are corridors, elevators, stairs, and sometimes rooms. Several sections may compose a complex-of-section (e.g. floor, Figure 4). A building is then an aggregation of sections and complexes of sections. Figure 4: Complex of section (two end sections and one connector section (left) vertical complex of section (subdivided with a virtual polygon, right) Figure 5: Semantic model for evacuation from buildings UML diagram represents the relations between the different types of polygons, sections and complexes of sections (Figure 5). Having the classification above, interesting interrelations can be observed. The type of polygons bounding a section has influence on (is related to) the type of section, i.e. only particular types of a polygon can be a part of some of the sections. For example non-granting polygons can be only real and close non-assessable sections only. Type of access and type of passing are critical polygon parameters for computing evacuation routes.