Abstract
Keywords:virtual materials, virtual prototyping, computer graphics, visualization, photorealistic images
We describe a measuring equipment and associated techniques for transferring the optical impression of real materials like leather, fabrics and car paint into the virtual world.
Currently, the creation of a computer generated picture is a creative but likewise technical process. Essential knowledge of the underlying 3d software package is mandatory. Numerous parameters have to be adjusted each and every time a picture with realistic impression is created. This is twice a challenging situation. First, there is a requirement for special knowledge in the field of computer graphics. Second, equally worse, it is the picture which should give a realistic impression of what the material applied on the future vehicle should look like and not the other way round.
This gave reason for Volkswagen to develop a virtual representation of a real material, a collaborative work of the computer graphics department at the University of Bonn and the research and development department of the Volkswagen AG. The virtual material has to satisfy a set of conditions, most significant one is the replication of the optical properties. Another constraint is the ease of application. Hence, no special computer graphics knowledge is required.
The process of creating a virtual material divides into several steps starting with an extensive measuring of the desired material. For any material, series of digital photos are taken under varying view and light directions using standard consumer cameras (cf. [2]). In the next step, special compression algorithms are employed to reduce the amount of data resulting from these pictures from several hundred gigabyte to a few hundred megabyte preserving the optical relevant information represented as a Bidirectional Texture Function (cf. [3]). The derived virtual representation of the material serves as the basis for the resulting piece of software, the shader. Thereby, the virtual material has to meet a crucial property. The measured real material is a flat square piece of about 10 x 10 square centimeter. The resulting virtual material must fit on any geometry part however long and curving it is.
The way to upholster a seat with leather in the real world is described in the virtual world by parameterization and synthesis(cf. [4]). These methods define the course of action a user can assign the virtual material to arbitrary surface representations used in automotive engineering. The combination of these techniques enables us to produce highly reliable photorealistic images even for high resolution images of the virtual vehicle. The process of transferring the real material into the virtual world can easily be integrated into the standard visualization process, a fact of significant importance. Likewise remarkable, any measured material can be assigned to any geometry for an arbitrary number of vehicle visualization projects.