Bedřich Beneš

Building reconstruction using manhattan-world grammars

We present a passive computer vision method that exploits existing mapping and navigation databases in order to automatically create 3D building models. Our method defines a grammar for representing changes in building geometry that approximately follow the Manhattan-world assumption which states there is a predominance of three mutually orthogonal directions in the scene. By using multiple calibrated aerial images, we extend previous Manhattan-world methods to robustly produce a single, coherent, complete geometric model of a building with partial textures. Our method uses an optimization to discover a 3D building geometry that produces the same set of façade orientation changes observed in the captured images. We have applied our method to several real-world buildings and have analyzed our approach using synthetic buildings.

Interactive terrain modeling using hydraulic erosion

We present a step toward interactive physics-based modeling of terrains. A terrain, composed of layers of materials, is edited with interactive modeling tools built upon different physics-based erosion and deposition algorithms. First, two hydraulic erosion algorithms for running water are coupled. Areas where the motion is slow become more eroded by the dissolution erosion, whereas in the areas with faster motion, the force-based erosion prevails. Second, when the water under-erodes certain areas, slippage takes effect and the river banks fall into the water. A variety of local and global editing operation is provided. The user has a great level of control over the process and receives immediate feedback since the GPU-based erosion simulation runs at least at 20 fps on off-the-shelf computers for scenes with grid resolution of 2048 x 1024 and four layers of material. We also present a divide and conquer approach to handle large terrain erosion, where the terrain is tiled, and each tile calculated independently on the GPU. We show a wide variety of erosion-based modeling features such as forming rivers, drying flooded areas, rain, interactive manipulation with rivers, spring, adding obstacles into the water, etc.

Inverse Procedural Modelling of Trees

Procedural tree models have been popular in computer graphics for their ability to generate a variety of output trees from a set of input parameters and to simulate plant interaction with the environment for a realistic placement of trees in virtual scenes. However, defining such models and their parameters is a difficult task. We propose an inverse modelling approach for stochastic trees that takes polygonal tree models as input and estimates the parameters of a procedural model so that it produces trees similar to the input. Our framework is based on a novel parametric model for tree generation and uses Monte Carlo Markov Chains to find the optimal set of parameters. We demonstrate our approach on a variety of input models obtained from different sources, such as interactive modelling systems, reconstructed scans of real trees and developmental models.

Visualization of Simulated Urban Spaces: Inferring Parameterized Generation of Streets, Parcels, and Aerial Imagery

Urban simulation models and their visualization are used to help regional planning agencies evaluate alternative transportation investments, land use regulations, and environmental protection policies. Typical urban simulations provide spatially distributed data about number of inhabitants, land prices, traffic, and other variables. In this article, we build on a synergy of urban simulation, urban visualization, and computer graphics to automatically infer an urban layout for any time step of the simulation sequence. In addition to standard visualization tools, our method gathers data of the original street network, parcels, and aerial imagery and uses the available simulation results to infer changes to the original urban layout and produce a new and plausible layout for the simulation results. In contrast with previous work, our approach automatically updates the layout based on changes in the simulation data and thus can scale to a large simulation over many years. The method in this article offers a substantial step forward in building integrated visualization and behavioral simulation systems for use in community visioning, planning, and policy analysis. We demonstrate our method on several real cases using a 200-Gbyte database for a 16,300 km2 area surrounding Seattle.

Authoring Hierarchical Road Networks

We present a procedural method for generating hierarchical road networks connecting cities, towns and villages over large terrains. Our approach relies on an original geometric graph generation algorithm based on a non‐Euclidean metric combined with a path merging algorithm that creates junctions between the different types of roads. Unlike previous work, our method allows high level user control by manipulating the density and the pattern of the network. The geometry of the highways, primary and secondary roads as well as the interchanges and intersections are automatically created from the graph structure by instantiating generic parameterized models.

Interactive Reconfiguration of Urban Layouts

The layout of an urban space is a complex collection of man-made structures arranged in parcels, city blocks, and neighborhoods. An editor for interactively reconfiguring city layouts exploits geographical information system (GIS) data and provides tools to expand, scale, replace, and move parcels and blocks while efficiently exploiting their connectivity and zoning. The ability to create, extend, and change a model of a large-scale urban environment is useful for a variety of computer graphics applications. For example, it lets urban planning applications simulate changes to city layouts or newly proposed neighborhoods, create hypothetical views of an urban area after applying development and growth algorithms, and show architects the results of using common building blocks to design a new city layout.

Interactive modeling of virtual ecosystems

We present a novel technique for interactive, intuitive, and efficient modeling of virtual plants and plant ecosystems. Our approach is biologically-based, but shades the user from overwhelming input parameters by simplifying them to intuitive controls. Users are able to create scenes that are populated by virtual plants. Plants communicate actively with the environment and attempt to generate an optimal spatial distribution that dynamically adapts to neighboring plants, to user defined obstacles, light, and gravity. We demonstrate simulations of ecosystems composed of up to 140 trees that are computed in less than two minutes. Various phenomena previously available for non-realtime procedural approaches are created interactively, such as plants competing for space, topiary, plant lighting, virtual forests, etc. Results are aimed at architectural modeling, the entertainment industry, and everywhere that quick and fast creation of believable biological plant models is necessary.

Urban ecosystem design

We address the open problem of spatial distribution of vegetation in urban environments by introducing a user-guided simulation and procedural system for integrating plants into the interactive design process of 3D urban models. Our approach uses as input 3D geometry of an urban layout from which it infers initial conditions and parameters of procedural rules. A level of manageability is calculated for each area of the urban space. The manageability level defines the amount of influence between the wild ecosystem simulation, where the plants compete for resources and seed freely, and the managed ecosystem, where nearly no seeding is allowed and the plants grow only under well-defined conditions. The wild ecosystems are handled by a simulation of plant competition for resources, whereas the procedural generation is based on an expandable set of behavioral rules of owners and typical plant management. Our system provides an interactive semi-automatic method to calculate a spatial plant distribution and to create an urban model with plants covering an area of several square kilometers in less than a minute. It provides a high degree of controllability and works tightly with an urban simulation system. We show various examples, such as plant development over time in managed and unmanaged areas, effect of procedural rules on the plant distribution, and the effect of changing the level of manageability and the plant distribution.

Augmenting heteronanostructure visualization with haptic feedback

We address the need of researchers in nanotechnology who desire an increased level of perceptualization of their simulation data by adding haptic feedback to existing multidimensional volumetric visualizations. Our approach uses volumetric data from simulation of an LED heteronanostructure, and it translates projected values of amplitude of an electromagnetic field into a force that is delivered interactively to the user. The user can vary the types of forces, and they are then applied to a haptic feedback device with three degrees of freedom. We describe our methods to simulate the heteronanostructure, volume rendering, and generating adequate forces for feedback. A thirty one subject study was performed. Users were asked to identify key areas of the heteronanostructure with only visualization, and then with visualization and the haptic device. Our results favor the usage of haptic devices as a complement to 3-D visualizations of the volumetric data. Test subjects responded that haptic feedback helped them to understand the data. Also, the shape of the structure was better recognized with the use of visuohaptic feedback than with visualization only.

An intuitive polygon morphing

We present a new algorithm for morphing simple polygons that is inspired by growing forms in nature. While previous algorithms require user-assisted definition of complicated correspondences between the morphing objects, our algorithm defines the correspondence by overlapping the input polygons. Once the morphing of one object into another is defined, very little or no user interaction is necessary to achieve intuitive results. Our algorithm is suitable namely for growth-like morphing. We present the basic algorithm and its three variations. One of them is suitable mainly for convex polygons, the other two are for more complex polygons, such as curved or spiral polygonal forms.