Pascal Müller

Procedural modeling of buildings

CGA shape, a novel shape grammar for the procedural modeling of CG architecture, produces building shells with high visual quality and geometric detail. It produces extensive architectural models for computer games and movies, at low cost. Context sensitive shape rules allow the user to specify interactions between the entities of the hierarchical shape descriptions. Selected examples demonstrate solutions to previously unsolved modeling problems, especially to consistent mass modeling with volumetric shapes of arbitrary orientation. CGA shape is shown to efficiently generate massive urban models with unprecedented level of detail, with the virtual rebuilding of the archaeological site of Pompeii as a case in point.

Procedural modeling of cities

Modeling a city poses a number of problems to computer graphics. Every urban area has a transportation network that follows population and environmental influences, and often a superimposed pattern plan. The buildings appearances follow historical, aesthetic and statutory rules. To create a virtual city, a roadmap has to be designed and a large number of buildings need to be generated. We propose a system using a procedural approach based on L-systems to model cities. From various image maps given as input, such as land-water boundaries and population density, our system generates a system of highways and streets, divides the land into lots, and creates the appropriate geometry for the buildings on the respective allotments. For the creation of a city street map, L-systems have been extended with methods that allow the consideration of global goals and local constraints and reduce the complexity of the production rules. An L-system that generates geometry and a texturing system based on texture elements and procedural methods compose the buildings.

Image-based procedural modeling of facades

This paper describes algorithms to automatically derive 3D models of high visual quality from single facade images of arbitrary resolutions. We combine the procedural modeling pipeline of shape grammars with image analysis to derive a meaningful hierarchical facade subdivision. Our system gives rise to three exciting applications: urban reconstruction based on low resolution oblique aerial imagery, reconstruction of facades based on higher resolution ground-based imagery, and the automatic derivation of shape grammar rules from facade images to build a rule base for procedural modeling technology.

Interactive procedural street modeling

This sketch presents a solution to efficiently model the street networks of large urban areas. Parish and Müller [2001] were the first to note that the street network is the key to create a large urban model. While this algorithm created a high quality solution, the method does not allow to incorporate user-control. To address this limitation we provide a rather different alternative to street modeling that allows to integrate a wide variety of user input. The key idea is to use tensor fields to guide the generation of street graphs. A user can interactively edit a street graph by either modifying the underlying tensor field or by changing the graph directly. This allows for efficient modeling, because we can combine high-level and low-level modeling operations, constraints, and procedural methods. The major contributions are as follows: (1) We are the first to introduce a procedural approach to model urban street networks that combines interactive user-guided editing operations and procedural methods. (2) We are introducing a new methodology to graph modeling in general. The idea of tensor-guided graph modeling together with the tight integration of interactive editing and procedural modeling has not been explored previously in related modeling problems, such as modeling of bark, cracks, fracture, or trees.

Interactive geometric simulation of 4D cities

We present a simulation system that can simulate a three‐dimensional urban model over time. The main novelty of our approach is that we do not rely on land‐use simulation on a regular grid, but instead build a complete and inherently geometric simulation that includes exact parcel boundaries, streets of arbitrary orientation, street widths, 3D street geometry, building footprints, and 3D building envelopes. The second novelty is the fast simulation time and user interaction at interactive speed of about 1 second per time step.

Modelling the Appearance and Behaviour of Urban Spaces

Urban spaces consist of a complex collection of buildings, parcels, blocks and neighbourhoods interconnected by streets. Accurately modelling both the appearance and the behaviour of dense urban spaces is a significant challenge. The recent surge in urban data and its availability via the Internet has fomented a significant amount of research in computer graphics and in a number of applications in urban planning, emergency management and visualization. In this paper, we seek to provide an overview of methods spanning computer graphics and related fields involved in this goal. Our paper reports the most prominent methods in urban modelling and rendering, urban visualization and urban simulation models. A reader will be well versed in the key problems and current solution methods.

Procedural 3D reconstruction of Puuc buildings in Xkipché

This paper examines how architectural shape grammars can be used to procedurally generate 3D reconstructions of an archaeological site. The Puuc-style buildings found in Xkipche, Mexico, were used as a test-case. We first introduce the ancient Mayan site of Xkipche and give an overview of the building types as distinguished by the archaeologists, based on excavations and surveys of the building remains at the surface. Secondly, we outline the elements of the building design that are characteristic of the Puuc architecture. For the creation of the actual building geometries, we further determine the shape grammar rules for the different architectural parts. The modeling system can then be used to reconstruct the whole site based on various GIS (Geographical Information Systems) data given as input, such as building footprints, architectural information, and elevation. The results demonstrate that our modeling system is, in contrast to traditional 3D modeling, able to efficiently construct a large number of high quality geometric models at low cost.

Procedural modeling for digital cultural heritage

The rapid development of computer graphics and imaging provides the modern archeologist with several tools to realistically model and visualize archeological sites in 3D. This, however, creates a tension between veridical and realistic modeling. Visually compelling models may lead people to falsely believe that there exists very precise knowledge about the past appearance of a site. In order to make the underlying uncertainty visible, it has been proposed to encode this uncertainty with different levels of transparency in the rendering, or of decoloration of the textures. We argue that procedural modeling technology based on shape grammars provides an interesting alternative to such measures, as they tend to spoil the experience for the observer. Both its efficiency and compactness make procedural modeling a tool to produce multiple models, which together sample the space of possibilities. Variations between the different models express levels of uncertainty implicitly, while letting each individual model keeping its realistic appearance. The underlying, structural description makes the uncertainty explicit. Additionally, procedural modeling also yields the flexibility to incorporate changes as knowledge of an archeological site gets refined. Annotations explaining modeling decisions can be included. We demonstrate our procedural modeling implementation with several recent examples.

Grammar-based encoding of facades

In this paper we propose a real‐time rendering approach for procedural cities. Our first contribution is a new lightweight grammar representation that compactly encodes facade structures and allows fast per‐pixel access. We call this grammar F‐shade. Our second contribution is a prototype rendering system that renders an urban model from the compact representation directly on the GPU. Our suggested approach explores an interesting connection from procedural modeling to real‐time rendering. Evaluating procedural descriptions at render time uses less memory than the generation of intermediate geometry. This enables us to render large urban models directly from GPU memory.

Rome Reborn

Rome Reborn (www.romereborn.virginia.edu) is an international initiative, started in 1996 and based at the Institute for Advanced Technology in the Humanities (IATH; see www.iath.virginia.edu), to create 3D urban models illustrating the development of ancient Rome from the first settlement in the late Bronze Age (ca. 1,000 B.C.) to the depopulation of the city in the early Middle Ages (ca. A.D. 550). Other institutional partners have included the Politecnico di Milano, UCLA, the Université de Caen, and the Ausonius Institute at the Université de Bordeaux-III. Commercial rights to Rome Reborn have been exclusively licensed to Past Perfect Productions s.r.l., a corporation based in Rome, Italy (http://www.pastperfectproductions.com/).