An Environment for Real-time Urban Simulation William Jepson’, Robin Liggett2, Scott Friedman3 Department of Architecture, UCLA ABSTRACT Drawing from technologies developed for military flight simulation and virtual reality, a system for efficiently modeling and simulating urban environments has been implemented at UCLA. This system combines relatively simple 3-dimensional models (from a traditional CAD standpoint) with aerial photographs and street level video to create a realistic (down to plants, street signs and the graffiti on the walls) model of an urban neighborhood which can then be used for interactive fly and walk-through demonstrations. The Urban Simulator project is more than just the simulation software. It is a methodology which integrates existing systems such as CAD and GIS with visual simulation to facilitate the modeling, display, and evaluation of alternative proposed environments. It can be used to visualize neighborhoods as they currently exist and how they might appear after built intervention occurs. Or, the system can be used to simulate entirely new development. SIMULATION INTERFACE Work at UCLA has focused on creating a user interface for viewing and interacting with a 3-dimensional environment which has been designed specifically to meet the needs of the planning and design professions. This interface and simulation software runs on a Silicon Graphics Onyx workstation with Reality Engine graphics hardware allowing extensive use of real-time texture mapping. The simulation software was developed using Silicon Graphic’s IRIS Performer application development environment. Using a Motif/X- Windows standard, the UCLA interface to the simulation includes a well-defined set of functions that most users will find sufficient for loading and viewing models without additional programming effort. However, the interface has been designed in such a way that it is easy to custom tailor the simulation to a particular application. The simulation interface includes fly/drive controls so that the user can travel anywhere and view any part of the model from a digitally accurate perspective. Dynamic objects (such as moving vehicles or lWilliam lepson. (310)825-5815. [email protected] ‘Robin Liggett. (310) 825-6294, [email protected] ‘Scott Friedman. (310)825-6294. [email protected] Department of Architecture, School of Arts and Architecture 1317 Perloff Hall. UCLA, Los Angeles. CA 90024-1467 Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the ACM copyright notice and the title of the publrcation and Its date appear, and notice is given that copying is by permission of the Association of Computing Machmery. TO copy otherwise, or to republish, requires a fee and/or specific permission. 1995 Symposium on Interactive 3D Graphics, Monterey CA USA 0 1995 ACM 0-69791-736-7/95/0004...$3.50 pedestrians) can be included in the scene. The user has the option of attaching to any of these objects as they are moving through the model allowing specific paths to be followed and evaluated. A separate mode of interaction allows three-dimensional selection (“picking”) of objects in the scene. Once selected, an object can be removed from the scene (simulating, for example, the removal of a building from a lot), or highlighted in the scene (as if a colored spot light were focused on it). More importantly from a design perspective, alternative models can be substituted for the object. This latter function is useful for displaying design options for a particular site, or showing a sequential set of options (for example, models that show the development of a site over time or the growth over time of newly planted foliage). Another key option in “pick” mode allows an associated data base to be queried for object attributes. This option provides the capability for dynamic query and display of information from an existing data base (for example, a Geographic Information System (GIS)) in a real time 3-dimensional format. THE MODELING PROCESS The simulation component of the system does not include capabilities for building the basic model geometry, rather it is used only for interactive viewing, manipulation and querying of the 3- dimensional model and associated databases. Software System’s MultiGen is the primary 3-dimensional modeler used in the modeling process. MultiGen, traditionally used for military applications, has the ability to quickly model an urban scene by the application of photographic images (“textures”) to highly simplified geometric models of objects such as buildings, trees, streets, etc. The model creation process begins with plan view aerial photographs which are a quick, easy and accurate way to obtain up- to-date information on street widths, building foot prints, foliage, etc. These photos are scanned into the computer and appropriately scaled and rotated to fit into the California State Plane grid coordinate system that is used for all Los Angeles projects. Using these photos as a base, streets and blocks are quickly identified, outlined and inserted into the database using MultiGen. In many cases detailed street, parcel and building plan data already exists in DXF format (for many areas of the City of Los Angeles, for example), which can significantly shorten this phase of the modeling. If a DXF file is available, the aerial photograph can be calibrated to the DXF plan. Generally modeling the 3-dimensional geometry of the existing buildings requires only simple rectilinear extrusions to the building 165heights, although mom detailed model construction is possible, The photorcalism of the model comes from the application of photographic textures to the simple 3-D forms. Textures are captured by video taping each building facade in the study area. This video information is fed directly into the computer, perspective and color corrected, and