# An Indoor Space Model of Building Considering Multi-Type Segmentation
## 1 Introduction  
Indoor space is an important part of the interior of the building, and it is the main place where people live their daily life. The life and work of modern residents are mostly in the indoor space of the renovated building, and the time spent has reached 80-90% of the whole day [1]. With more and more environmental simulation and application analysis of indoor scenes, the spatial organization of buildings, floors, and rooms is difficult to meet the needs of refined and diversified indoor space analysis. It is mostly because some types of information required by certain applications do not exist in the current models and standards, for example, a more detailed subdivision information of the indoor space model framework is required in indoor navigation analysis [2, 3, 4]. Describing and expressing these micro-scale indoor spaces is the core issue of current indoor GIS research, which is conducive to assisting in sophisticated social management and application analysis of human settlements [5, 6]. With the acceleration of urbanization, many scholars and institutions in the fields of geographic information and building information engineering have done a lot of research on the indoor space model of buildings [7]. Several specifications for building spaces have also been widely concerned, and the most prominent are considered include CityGML, IndoorGML and IFC4.3 [8, 9, 10]. In this study, we summarize related studies and specifications into two categories: focusing on the expression of entities and focusing on the expression of spaces themselves. The first category is the indoor space model which focuses on theexpression of entities. The defined various component entities are used to represent the actual building structure and its indoor entities, which mainly include building components, indoor furniture, home appliances, and other components [11]. The components are all tangible things that exist physically in the real world and are used to create an enclosed function space for use. CityGML supports the description of city objects from semantics, geometry, and topology. As one of the most detailed themes defined in CityGML 3.0, the building extension module allows building elements to be represented with four levels of detail from LOD0 to LOD3. The current version of CityGML 3.0 only regards the smallest granular indoor space type as the feature (Room), and internal facilities such as furniture can be represented in all LODs 0-3. As the indoor environment for human activities becomes more and more complex, the inadequacies of CityGML's building model in expressing indoor elements are more obvious. Therefore, researchers have developed a series of indoor extension models ADE to support these indoor applications [12; 13; 14; 15; 16]. [PERSON] et al. (2018) proposed an extended indoor multiple levels of detail (ILOD) specification, especially for indoor spaces. ILOD takes advantage of the two existing international standards (IFC and IndoorGML) to extend the existing LOD4 of CityGML 2.0 into a more accurate indoor ILOD0-ILOD4. [PERSON] et al. (2017) developed CityGML ADE for indoor routing and positioning. It adds indoor elements related to this application field and enriches BuildingInstallation elements to support indirect connections between floors, such as stairs and elevators. CityGML focuses on the element model rather than the spatial model. [PERSON] et al. (2013, 2014) are committed to enhancing the expression of indoor elements of CityGML 2.0 and developed Indoor ADE, which extends the indoor element models of two building modules: indoor facility element models and indoor space element models. The former includes tables, chairs, and interior components such as fire hydrants, while the latter is functional space elements such as offices and conference rooms. At the same time, the ADE is only based on CityGML LOD4, and the main feature is that it can support the description and expression of the building story.