Inverse-Procedural Methods for Urban Models

Procedural modeling is an elegant and fast way to generate huge complex and realistically looking urban sites. Due to its generative nature it can also be referred to as forward-procedural modeling. Its major drawback is the usually quite complicated way of control. To overcome this difficulty a novel modeling paradigm has been introduced: it is commonly referred to as inverse procedural modeling, and its goal is to generate compact procedural descriptions of existing models—in the best case in an automatic manner as possible. These compact procedural representations can be used as a source for the synthesis of identical or similar objects, applied in various simulations and other studies of urban environments. We believe that this technology is still a widely unexplored ground and that it will prove itself as a very important tool in the reconstruction process. In this paper we sketch how inverse procedural modeling can be applied in the urban modeling field. Introduction. Nowadays, modeling and reconstruction of urban environments has become an estimated multi-billion dollar industry. The reason for this progression is the wide range of possible applications, including cyber-tourism, computer games, and the entertainment industries in general, all of which have recognized the potential of virtual worlds. The generation of large urban environments has been a key aspect of several recent computer games and movies [Sey12], with modeling times reaching several man years. Furthermore, the digital maps industry has become ubiquitous and can be encountered in many everyday usage items like mobile phones and cars. Besides entertainment-inspired applications, city planners, local governments, and scientists are also using advanced three-dimensional simulation and visualization software to plan and manage cities. Urban reconstruction is an interdisciplinary task that spans multiple fields. A recent survey [MWA∗13] reviews the work done in computer graphics, computer vision, and photogrammetry and remote sensing. A significant contribution of the computer graphics community brought into this topic is procedural modeling. Traditional procedural modeling introduced over a decade ago [PM01] is an elegant and fast way to generate huge, complex and realistically looking urban sites. Another survey [VAW∗10] presents an overview over that topic. The major drawback of this technique is, however, a rather complicated way of control. In order to generate a rich and plausible city model the procedural system requires a large Input Low Level: Imagery LiDAR Polygon Soup Higher-Level: Segmented Annotated Models Inverse Procedural Engine Procedural Engine Output