Abstract: Mobile indoor navigation systems guide users through buildings and premises by taking into account the current position of the user and a destination such as a room, office or shop. In many environments a spontaneous and also anonymous navigation is desirable e.g. at airports, hospitals or university campuses. However, many systems that have been proposed so far require the integration of a radio-based positioning system and access to other organization-specific systems, which results in a lot of things a user has to deal with before the navigation system can be used and which raises a lot of issues with respect to the location privacy of the user. In this paper we propose a mobile indoor navigation system that allows spontaneous navigation and that guarantees location privacy for the user. A pre-compiled compact representation for all the routes and navigation instructions in a building is the basis for an application that uses the built-in camera on the mobile device to der...