## 2 Related Work  
One of the first approaches towards an indoor navigation system was the so called _Cyberg guide_ system [17]. It is designed as a tool for guiding tourists through both outdoor and indoor environments. When entering a new room inside a building, the system indicates this by displaying an arrow on a two-dimensional map.  
Similarly, the _MARS_ System [18] provides information about buildings in the Columbia university campus to the users (e.g., visitors, staff, students, _etc._). It is a collaborative system in which users can annotate obstacles or buildings and share this information via a desktop or augmented reality. A similar system for the Ecole Polytechnique F d'\(\acute{\text{e}}\)rale de Lausanne (EPFL) is presented in [19], whereas a two-dimensional map is utilized for visualization.  
The user-oriented development of a nomadic exhibition guide for trade fair visitors is described in [20]. Within the _SAiMotion_ project, the authors developed a system which supports planning at home as well as mobile guidance on-site--both in a 2D map. A similar prototype for an exhibition show guiding application is also presented in [21].  
One of the first 3D applications is described in [5]. As a prototypical system the authors utilized Oracle Spatial 10 g (with a mixed model of geometry and graph) as DBMS and the building of the Aerospace Faculty of TU Delft (with 13 floors) as a test building. The graph contains about 1200 elements.  
An indoor navigation system, namely _iNAV_, is presented in [22]. It uses the A* algorithm for real-time routing and navigation. The Java client is suitable for laptops or proper PDA devices. The system consists of several distributed web services. An initial trial by the authors has revealed a lack of performance due to service communication. A similar approach with client-server architecture based on PHP (_i.e._, programming language for dynamic web applications, namely Hypertext Preprocessor) web services and KML (a XML-based markup language for Geodata, namely Keyhole MarkupLanguage) models is also presented in [23]. Similar mobile solutions (mostly in 2D) are furthermore available [24, 25, 26].  
In [27] the development of an indoor navigation system which considers users' special needs and preferences, is described. It aims at the provision of universal indoor LBS for everyone and therefore tries to support several types of users by exploiting multimodal interaction. Unfortunately the path algorithm used for route calculation \"_can only be applied to connected two-dimensional digraphs, which means the route can be computed only if the O and D are located on a connected single floor_\" [28]. Another 2D indoor navigation framework is also presented in [29, 30].  
Besides those research-motivated indoor routing systems, there are also some web-based indoor maps developed by global companies such as Google Indoor Maps [2], NAVTEQ Destination Map [4], or Bing Maps Venue maps [3], but these only utilize two-dimensional data for the visualization.  
To conclude this brief review, it becomes apparent that both research and economy develop different solutions for indoor maps and routing. However, existing solutions are mainly two-dimensional, although it has been demonstrated that a 3D visualization is advantageous [6]. Furthermore, existing 3D applications require additional software or plugins, thus a broad application on standard browsers is not possible. That is, users have to download and install additional software, representing a barrier for the utilization of the service. However, regarding the future Internet, a ubiquitous accessibility of such standard-based services is desirable. Regarding the data of the above mentioned applications, it becomes obvious that they all utilize proprietary data. In most cases license fees have to be paid for those, because they have typically a cost recover model for the data acquisition. Essentially, as far as the author is aware, there is no 3D indoor map and routing application available, which utilizes crowdsourced geodata.