Chapter 7: Visualization/Simulation Technologies

Historically, the process of transportation and land use planning involved the understanding and use of space as a two-dimensional entity. In a two-dimensional spatial setting, two axes (x and y) are used to provide surface dimensions (length and width) for a given area. Master plans and transportation projects were portrayed in a flat, two-dimensional style. Various forms of photosimulation were employed to provide a two-dimensional interpretation of future conditions and the visual effects of transportation improvements.

Several factors began to influence our spatial point of reference. Computers and graphics technology first applied to the entertainment film industry, and the military establishment brought about a changing paradigm. Space flight, aerial reconnaissance, and GISs motivated the shift from two-dimensional (2-D) to three-dimensional (3-D) perspectives. Industrial applications of CAD/CAM in product development and manufacturing also pushed the spatial envelope. Meteorology, beginning with upper atmospheric characteristics of movement, temperature, weather conditions, and air quality, changed the boundaries of the earth’s biosphere.

Motion-based imagery in the development of animation for film (e.g., cartoons) created the first synthetic environments, which led to development of special effects. Computer animation expanded the number of applications into the gaming and entertainment industry. Animation, however, is not simulation because it does concern itself with visual accuracy and engineering precision. Nonobject-oriented technology is now being supplanted by object-oriented imagery, and computer-based simulation is recognized as a valuable tool to assist engineers, architects, and planners in their professional practice.

New 3-D and four-dimensional (4-D) technologies are now readily available for improved analysis of transportation projects. Experiments with a number of additional simulation technologies are under way (such as aerial, subsurface, multi-sensory, multi-variant, social and physical, and real-time operations simulation) and may be readily available in the near future for transportation applications.

The evaluation will focus on two interrelated technologies:

• 3-D simulation
• 4-D simulation

The quality of the simulation and its suitability for various applications are controlled by four characteristics or variables: navigation, eye points, graphics capability, and fidelity. These variables are relevant to the application of both 3-D and 4-D simulation technologies.

Navigational simulation addresses how the user "travels" through space, the form of interactivity with the scene generation or visualization. The simplest navigational form involves using the mouse or keyboard; movement is directly related to the position of the mouse or the depression of various keys. A touch-screen or electronic stylus can be used to enhance the navigational process. Computer-based visually wired accessories, such as computer gloves and helmets, allow the user to "enter" the scene. To more accurately mimic the transportation experience, "person in the loop" scenarios can be developed using a cockpit (e.g., automobile, bus, truck, train, aircraft, or ship) as the navigational device; a steering wheel with accelerator and brake provides the user with capability to "move" through space.

The eye point represents the user’s view of the simulated scene. In a comprehensive digitized database visualization, where the eye point is coupled to motion, the resulting "fly-through" can offer a 180-degree to 360-degree point of reference. An aerial vantage point, oblique view, cross section, and frontal perspective can be presented in rapid succession. In terms of understanding roadway alignments, it can provide a cross-section perspective from the living room window of a residence as well as an at-grade view from a traffic lane. Eye points can permit the user to be inside a home, school, or hospital or outside. It can place the individual inside a moving vehicle, stopped at an intersection, or simply in a bird’s-eye view looking down at a proposed construction site.

Graphics for producing a simulated visualization can be generated from many sources. Historically, photography was used to provide realistic texture to a computer-enhanced scene. Digital imagery now provides more flexible and accurate renderings. GIS, including topographic and terrain mapping combined with CAD-based facility design information, assists in developing an accurate graphical scene. 3-D-based rather than 2-D-based information facilitates the simulation development and the resulting accuracy. Most simulation software packages include an array of standard images (trees, street furniture, etc.) that can be imported into the scene.

Display technology is another important element of the motion-based simulation. The scan size of the graphic image should be 640 by 480 at a minimum. Depending upon the number of channels/pipes used in the simulation, the scan size can be extended to 800 by 600, 1024 by 768, or 1280 by 1024.

Projection systems for these simulations begin with computer monitors (front screen or rear projected) in a variety of sizes. Overhead electronic projections are capable of creating large scenes on wall surfaces, screens, or domes. One of the more advanced simulation projection systems is a CAVE (Cave Automated Virtual Environment) that can also provide synchronous sound.

The fidelity or the accuracy of the created simulation is of primary importance. If it doesn’t look "realistic," the user has little confidence in the simulation. In terms of motion-based simulation, a 60 Hertz per second frame rate is required to provide a smooth, continuous image. This industry standard represents the threshold of acceptable visual acuity for animation. At a frame and refresh rate below 60 Hertz, the observer can start to detect a discontinuous, staggered, or flickering image.

The level of accuracy can also be affected by the choice of operating system and graphic software. Operating systems including NT, SGI, SUN, HP, and Linux-based platforms can all be used successfully.

Computer-based simulation allows creation of a 3-D, motion-based visual environment. This 3-D environment relies on three spatial axes (corresponding to the dimensions of length, height, and width) to create a spatial scene. The image is visually created in a computer graphic format, including the capability of incorporating motion as part of the scene generation. Other senses (particularly sound) are beginning to be synchronized to such simulations.

This 3-D technology is most commonly used to depict future visual scenarios relating to proposed transportation projects. The capability to operationalize data to replicate accurate present and projected conditions is rapidly evolving. For example, the first 3-D applications were animations of traffic counts or average daily traffic. Now, both software and hardware have advanced to enable accurate simulation of traffic capacity. This operational refinement allows use of simulations in the planning process, including developing and analyzing alternative solutions.

New York Route 110 Intermodal Transportation and Land Use Study: The primary goal of this study for the New York DOT was to identify options to reduce personal vehicle use in the Route 110 Corridor in the middle of Long Island. The study examined both transportation and land use practices using a three-dimensional computer-based simulation. A preliminary visualization tool—a video-based simulation of a significant intersection in the corridor—was used to inform the towns of Huntington and Babylon about the uses of visual simulation as a land use and transportation planning tool. Realistic traffic flow was correlated with the visual scene and presented in a live interactive session. This application also sets the stage for four-dimensional master planning—that is, including the element of time in simulated integrated transportation and land use planning.

Three-dimensional visualization is an outstanding technology for increasing meaningful communication with process stakeholders about existing conditions, potential solutions, solution impacts, and mitigation options. Use of visualization tools increases the effectiveness of public involvement activities by creating better understanding of plan and project parameters than can be accomplished through traditional 2-D graphics and planimetric drawings. This, in turn, tends to expedite the plan or project development process and build support for its outcomes. Visualization products also provide broadcast-quality products suitable for media dissemination. In addition, the products can be used effectively in multi-media presentations and collaborative decisionmaking forums throughout the process.

Although technical expertise in this technology is quite limited, it is expanding as interest in the technology grows. Hardware and software costs, combined with the need for special-purpose staff, are generally viewed as the most significant limitations for in-house agency development of visualization capabilities. System compatibility issues for integration of visualization products are also cited as a limiting factor, although standards are being developed to eliminate many of these difficulties. Even assuming that the infrastructure and staff are in place to provide visualization services, the cost of preparing individual products is high and must be evaluated in terms of their value for the specific plan or project application.

Four-dimensional simulation adds the variable of time to 3-D simulation. The time variable permits heuristic examination of spatial change. Real-time analysis provides insights for traffic management, safety analysis, environmental change, construction management, and master planning (e.g., short range versus long range). Applications for design of transportation alignments in a "virtual reality" setting incorporating a full set of environmental features are anticipated. Time-based visual simulation is not as advanced as 3-D simulation, and consequently it is less common.

La Guardia Airport Transit Access Study: This 1-year "visual impact assessment" study being conducted for the New York Metropolitan Transit Authority is examining potential noise and visual/aesthetic attributes of alternatives for new subway access between the borough of Queens and La Guardia Airport. Given the project’s location in a dense urban area, noise and visual impacts are of primary concern. Four-dimensional virtual design techniques are being used to visualize impacts from a number of nodal "eye points," including the driver of the train, residents and occupants of buildings near the train, prospective passengers at the airport, views from nearby vehicles, and aerial views. Users of the assessment will include the project design team, the project sponsors, elected officials and other stakeholders, planners and community members, and the media. Participants in the collaborative design process will be able to experience the potential visual and noise impacts of the various alignments and elevations (above, below, and at-grade).

Benefits of 4-D visualization are similar to those identified for 3-D visualization but include additional value in applications for safety evaluation of roadway design, operational analysis, construction management, and other types of evaluation that benefit from addition of the temporal element. The "virtual reality" experience generated through this technology can be very important for developing increased stakeholder understanding of complex projects and their interactions with urban environments. 4-D visualization is also valuable for clarifying the phasing of complex projects that will be developed in stages over a long period of time.

Limitations for implementation of this technology are greater than those described for 3-D visualization in that there are fewer trained experts in its application and no infrastructure standardization. This is an emerging technology; application is largely experimental at this time.