Procedural Façade Textures for 3D City Models

The use of 3D city models has been introduced into a variety of fields from urban planning to disaster management. These models are no longer regarded as ‘simple’ visual representations of the real world; they act as an information space and as semantic models for urban environments as they represent much more than the visual appearance of the real world. For users of these ‘rich’ models the Level of Detail (LoD) in which the information is presented is essential for the ability to fulfil their specific task. Photo-realism is not always required or appropriate and non-photorealistic appearance [1] (e.g. artificial transparency, etc.) can be a much better support for users. One example is pedestrian navigation where 3D renderings help users to navigate. In this scenario visual similarity of objects is sufficient for the navigation task. Therefore a LoD is not always a representation of the capabilities of the data provider, but even more an appropriate rendering for the specific scenario in which the model is used [4]. These LoDs are well represented for geometry in standards like CityGML [2], but textures are still static and fixed, although they can carry a vast amount of information without increasing the geometrical complexity of the model. In this paper we will present a flexible procedural concept for façade textures that is based on tiles. These tiles are arranged according to a description to rebuild the façade texture. The description in our case is composed by ‘pulse functions’ [6] arranged in layers to define ‘active zones’ in the façade where specific elements need to be placed. The layers allow to group elements of same type, like windows, doors, etc. and to integrate specific layers into the façade description in order to built appropriately detailed façade textures. Besides the definition of the ‘active zones’ the description can also include additional attributes in order to define certain behaviour. One example would be to change the texture according to the distance of the user in a specific context. Another benefit of the procedural approach is that the texture can be rebuilt using modern graphics hardware with programmable rendering pipeline (shader).