Seeing the Light (Productivity Corner MicroStation Tutorial)1 Mar, 2007 By: C.J. Angus and J.A. Bryant,E.J. Stephens
The virtual railroad is the new technique for modeling signal sighting and layout.
The rail industry now faces a fundamental challenge: how to make signaling systems more efficient. For a signaling system to work effectively, a number of different components must work together -- electrical and electronic systems, logical design and software, layout of signals and signal sighting and interaction between signals and drivers.
Historically, the first two items have been subject to much study and analysis. Over the years, this approach has delivered very reliable signaling systems. Recent events, however, have highlighted the need to focus more on the latter items, namely the location of signals and the way in which they are interpreted and understood by the driver. Doing so has proved to be a considerable challenge as the traditional techniques for signal sighting and route learning are hard to deploy.
Signal sighting has required on-site location of signals, which has proved to be tricky because substantial changes are occurring. Likewise, route learning has proved difficult because the new layout cannot be driven until it has been constructed -- and even then, it isn't always possible to pass along each of the possible routes.
These problems have required the industry to devise a new means for establishing signal sighting and providing a mechanism for communicating the design to those who must understand and use it, namely the drivers. To be effective, the new approach has to place signals by parametric design rules, perform objective assessment of sighting, allow subjective assessment of sighting within the environment and communicate design.
Example of computer model (Heaton Chapel, Manchester, England).
3D Railway Models
The solution is to build a computer model of a railway that is a mathematical representation of the world in 3D, including a wide variety of features such as formation, earthworks, bridges and tunnels, platforms and stations and adjacent buildings, track and OLE (overhead line engineering). The model is populated with signals in their true spatial position by building a 3D digital model of surrounding features, track and OLE; placing signals; performing signal-sighting calculation and displaying results.
From this model, output can be generated to communicate the design in a variety of forms depending on users' needs -- drawings for design engineers, wire line diagrams for design engineers, static images for external users, animations for external users and interactive viewers for design engineers and drivers' subjective assessment.
The most important feature of the solution, however, is that it should be a seamless process yielding a single data model of the railway, generally known as a virtual railway. The virtual railway is a 3D computer model that can accommodate all of the common features that make up a railway. Each data type can be represented as an object. For example, track is divided into plain line, switch and crossing components. These objects can be displayed in a number of different ways depending upon user requirements.
The track model can be output in a variety of different forms, including component list, true-to-scale plans, track schematics, track profiles, cross sections, wire line views and 3D images. All of the different objects combine to form a complete railway model that can be analyzed and viewed at will.
The delivery of the solution requires a variety of software components:
- a 3D string modeler for terrain, track geometry, earthworks and overhead line;
- a solid modeler for structures and buildings;
- a rendering engine to create high-quality still images and animations;
- a viewer system for quick visual assessment of the design;
- a simulation system for communicating the design to the drivers and
- a signal placement and sighting tool.
Example of the objects in a virtual railway model (Stockport, England).
All of these components must be integrated seamlessly to work from a single data source and, thus, guarantee precision and currency of information. Of course, even if this goal is achieved, the problem of obtaining data to build the models still remains.
The models are built in a manner that simplifies the process of change. In general, there is a static model, which consists of the surrounding terrain, buildings adjacent to the track and earthworks, and a semi-static model, which comprises the rails and overhead line. This model contains the features that are updated on an intermittent basis and may require some work in the data conversion processes.
The final model is a dynamic model, which holds the signals. This model is automatically updated by the signal-sighting software as each signal is placed. In this way, it is possible to substitute changes in the track or OLE easily and to update the signaling layout immediately as design decisions evolve.
Example of signal-sighting tool.
How to Find the Data
A wide variety of data sources are available to build the models required, and their use depends upon the level of precision required in the end result. For example, it's reasonable to use ordinance survey mapping as the basis of the terrain model. Although this data source has known limits in terms of its precision, it has the advantage of being available for the whole of the railway network. If suitable tolerances are allowed in the objective analysis of signal sighting, it's acceptable to use this data. When greater precision is required, a more detailed survey would be carried out either in the form of aerial photography or ground survey.
The overhead line models can be constructed from as-built records or from on-train measurement systems. Likewise, the shapes for tunnels and overbridges can be established from gauging records or volumetric scanning survey. The information for the existing signaling layouts generally is derived from records or from survey data. Two types of information are required: the location of the signal and its configuration.
A number of different software tools are used to meet the signal-sighting requirements, including placing signals, performing calculations, creating flight lines for driver's eye position and interacting with the viewer. The signal placement tool allows designers to create signal objects in the 3D model and to configure the signals. The tool allocates the signal ID, composes the signal from components, places signal in 3D model and sets signal direction and dip. Once these variables have been assigned, it's possible to create a new signal in the 3D model and immediately view it in the viewer system.
Users then can change the signal or any of its attributes -- bearing, height or dip, for example -- at will and immediately see the effect of the change in the viewer. In this way, it's very simple to refine the placement of the signal to avoid problems such as read-through or obstruction by other equipment.
The performance calculations tool allows users to perform intervisibility calculations based on the location and direction of signals, obstructions and the driver's eye flight path. The objective is to show where there's obstruction to the signal and where there's potential for read-through. The tool creates rays for line of sight, calculates obstructions and four- and seven-second points, indicates a possible read-through locations, establishes a reserved signal volume and creates signal-sighting forms. The line-of-sight calculations take into account the conicity of the signal lamp lens and the viewing angle for the driver's eye, constrained with the viewing angle of the cab window.
An obstruction calculation is performed for the obstruction of features rising from the terrain (typically buildings and masts) and features dropping from above the line of sight (for example, bridges, tunnels and OLE). This process is repeated for each point along the flight line for the driver's eye, typically every 10 meters. At each point, each lamp within the signal is checked.
Lines showing the rays from the signal to the driver's eye position are generated in 3D and can be viewed in plan or wire-line perspective. Based on the 3D rays, a reserved volume can be established for the signal, with a nominal margin, into which no obstruction can be placed without reference to the signaling engineer. The final product of this process is the signal sighting form with the basic details for the signal filled in automatically.
In normal operation, the static model of the surrounding buildings and the semi-static model for track and OLE are read into the viewer. The signal design model is then passed dynamically to the viewer. As signals are created, modified or deleted in the 3D model, the interactive view is automatically updated.
Passing the data to a full rendering engine can create still images and animation. The ray-tracing functionality allows users to generate images with shadow and reflectance. This functionality produces a more realistic effect and produces images that are suitable for presentations, as opposed to the engineering-assessment quality produced by the interactive viewer.
The downside of using this type of system is the computational power required to generate the images. Each frame of an animation can take approximately 1 minute to generate, and a smooth animation requires a minimum of 25 frames per second. Thus, a 30-second animation sequence can require many hours. Should any changes to the animation be required, the animation usually will need to be rerun. So although this method does not lend itself to the interactive assessment of signals, it's ideal for display of the completed work.
The generation of high-quality still images can be achieved using the rendering engine to create large images. It's possible to include shadow, reflectance, fog, cloud, bright sunlight and many other characteristics. Again, each of these added features requires additional compute time, and, in some instances, a very complex still image can now take only a few minutes to render vs. a few hours.
The data generated for the interactive viewer is available in an industry-standard format that's widely used for visualization and simulation systems, so it's possible to upload the models into a simulator for route familiarization. The alternative is to use the interactive viewer in stand-alone mode, which allows users to select various train paths and set signals as required. Either approach builds on the same base data set used for the design of the signals without the need to reconstruct the data in a new system.
Trains moving in the simulator.
The benefits of this approach are many. From a practical and safety perspective, it reduces the number of visits required to site and reduces the number of possessions required and the frequency of staff going onto the track. From a quality-assurance point of view, this approach gives a continuous and traceable source for the data on which any decisions are based and will help to eliminate the possibility of out-of-date information being used.
From the cost side, the benefits are substantial not only in time saved by reduced site visits (though users still will need to confirm that the computer model is correct) but also from reduced reworking as most of the problems with placing signals in the railway environment will be resolved during the design phase using the interactive viewer.
One of the key features of this approach is the speed with which it's possible to achieve results. The interactive viewer allows the immediate display of anything that has been built to date. Thus, it's possible to start building models around a local area of interest and then to expand this at will, unlike animation where the modeling of the whole project must be completed before any animation can occur.
Where changes or additional information is required, it can be added to the model on an as-required basis and then immediately passed to the interactive viewer. After completion of the project, full animations and stills can be produced for communication of the design to a wider audience, including regulatory authorities and the public. Likewise, the data can be passed to train-operating companies for route learning.
This approach to signal sighting has proven to be a great success. For the first time, it's been possible to directly link the design process and its objective analysis with the subjective analysis and route learning available through the interactive viewer to provide a complete solution.
About the Author: C.J. Angus and J.A. Bryant
Autodesk Technical Evangelist Lynn Allen guides you through a different AutoCAD feature in every edition of her popular "Circles and Lines" tutorial series. For even more AutoCAD how-to, check out Lynn's quick tips in the Cadalyst Video Gallery. Subscribe to Cadalyst's Tips & Tricks Tuesdays free e-newsletter and we'll notify you every time a new video tip is available. All exclusively from Cadalyst!
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