Roads

Data Representation of Road Networks

• the most common sources of road data are centerlines, which are described by Vector data formats
• network topology is generally stored by representing the intersections as Nodes, which reference, or are referenced by, the road segments which connect them
• in some cases roads are also modelled as:
  • linear edges indicating the location of a curb or pavement edge
    • example: the GIS data of the City of Palo Alto
  • polygonal extent of road area
    • example: Transportation features layer of New York's NYCMap
• software tools for traffic simulation (see Vehicles) each have their own representation and file formats, e.g.:
• UNETRANS
  • an ESRI Transportation Data Model, apparently in conjunction with NCGIA (UCSB)
  • not a file format, but a recommended data organization to allow sharing of data
  • three optional representations for "road":
    1. Single centerline - for one roadway, regardless of lanes, etc.
    2. CarriageWay representation - one centerline per set of lanes going the same direction
    3. Lane representation
• the UK's OS MasterMap contains "themes" including "rail", "roads, tracks, and paths", "road network", and "road routing information"
  • these are only briefly described in their user guide, and need to be investigated further
  • presumably, they are GML2 profiles
• LandXML
  • a consortium and standard for very, very detailed road descriptions, down to specific physical properties of the road surface, precise curvatures, and exact profiles
  • this is a level of detail which is needed for some kinds of safety analysis, but is overkill for general modelling and visualization needs
• EDF - Environment Description Framework
  • a transportation network representation developed by Pete Willemsen of the University of Utah
  • described in Behavior and Scenario Modeling for Real-time Virtual Environments (pdf)
  • additional info in Ribbon Networks for Modeling Navigable Paths of Autonomous Agents in Virtual Urban Environments, 2003 (pdf)
  • allows for very detailed modelling of intersections, while astutely observing "Intersections are logically complicated, messy, and notoriously difficult to model, both geometrically and behaviorally."
• GDF
  • "Geographic Data Files", a specification for encoding transportation networks primarily with the purpose of trip planning, vehicle navigation and map display
  • it is mentioned as being in use by "intelligent transportation system" companies like TeleAtlas and NavTech, and you can currently buy some European road data in GDF format
  • amazingly wide scope - besides roadways, it supports encoding public transit, waterways, road signs, and much more
  • it was apparently granted status as standard ISO/TR 14825:1996 which corresponds to version 3.0 of the GDF, reportedly attempts are underway to bring the ISO up to date with version 4.0, but i cannot find any online description of 4.0
  • the GSDI Geospatial One-Stop site has a document on Data Content Standards For Transportation: Roads (pdf, April 2003) which references GDF along with many other systems
• the GSDI Geospatial One-Stop site has a page on Transportation Standards
  • has separate documents for Road, Railroad, Transit, Air, and Waterway
  • these 'standards' have had the input of U.S. federal agencies, ESRI, and other commercial companies
  • it is hard to tell if these are guidelines or specifications, whether they augment or conflict with other specs such as UNETRANS or GDF, and whether and how people are expected to utilize them
• rough, incomplete comparison table of several road representations
• OpenStreetMap.org
  • an effort to produce free (CC licensed) streetmaps of the world, which includes a mailing list with a lot of good discussion on road data formats
  • related MapOntology wiki at the UO Faculty of Cartography

Data Representation in Traffic Simulation Software

Traffic sim software is also listed on Vehicles and Traffic.
Here are notes on how the software relates to data storage.

• Trafficware Synchro Studio / SimTraffic is a popular commercial package
  • however its road network format is totally undocumented (?)
  • there is one mention online says with 'the UTDF capability, the user can also easily export the data to Passer II, CORSIM, Transyt-7F or Highway Capacity Software.'
  • SimTraffic uses another proprietary format called '.s3d' to transfer a scene description to its 3D Viewer.  Back in 2003, the company wrote "when version 6 was created, we developed this s3d format so others could write software to view this. However, there really haven't been any viewers that have been made available." [ref]  They then introduced their own viewer in their version 7.  Perhaps this implies that .s3d is designed to be openly readable?
• Paramics
  • A commercial suite of software tools for microscopic traffic simulation developed by Quadstone Ltd.
  • Has some documentation for its structures and formats in the reference material on the page Paramics Technical Support Documentation.  Specifically, section 18.2 in Appendix B in their Modeller Reference Manual V4 (zipped pdf) - data "primarily associated with the physical attributes of the road network"

Generating 3D Roads

• the idea is to go automatically from a 2D road description to a completely 3D polygonal road
• two main approaches: draped vs. merged
  1. thin geometry draped on top of the terrain
     • pro: simpler and faster, easily changed at runtime, allows the terrain to be a regular grid
     • con: "Z-buffer fighting" due to overdraw
       • there are ways to reduce the Z-buffer problem
  2. roads merged into the terrain ("stitched", embedded)
     • pro: flawless road boundaries, no overdraw issues
     • con: requires computationally complicated and slow preprocessing
     • all known commercial programs (see below) prefer this approach
• with either approach, an algorithm is needed to convert road centerlines (raw vector data) to a full 2D/3D representation
  • there are no known published algorithms for doing this!

Implementation of Roads in the VTP Software

Commercial Road-Building Software

• Terrex TerraVista
  • can drape or stitch (merge) roads onto terrain
  • reads centerlines from DFAD, DLG, LULC, and ArcInfo Shape files
• MultiGen Creator Terrain Studio and RoadTools
  • adds embedded roads, rivers, urban areas, trees to OpenFlight terrain
  • "multiple polygonalization algorithms, variable simplification constraints and polygon limits allow rapid database production"
  • reads centerlines from DFAD, DLG, and LULC
  • RoadTools costs around $10,000, plus you need to have MultiGen already
• RoadViz
  • $500 for Windows from My3D LLC, see more about it on Commercial Terrain Tools
   
• several other high-end packages and consulting services offer some road functionality; there are no known affordable tools or open implementations

Games

• most sophisticated so far: Angel Studio's Midtown Madness (1999) had 100km of roads (downtown Chicago), which were procedurally generated then touched up with hand modelling
• most racing games (e.g.. SF Rush) have hand-modeled roads, not procedurally generated
• Streets of SimCity by Maxis/EA did road generation, but it only did straight, simple roads with very artificial data

Notes

• a page on Intersection Construction by Rachel Nador
  • uses MultiGen
  • has lots of great information, much of which is applicable to procedural construction
  • a page with more detail on a related project (COOP5) seems to have vanished from the CCAD site
• other road resources
  • Public Roads is the bimonthly magazine of the Federal Highway Administration (FHWA), U.S. DOT, created at the Turner-Fairbank Highway Research Center (TFHRC)
  • Bureau of Transportation Statistics (BTS)
  • Caltrans Highway Design Manual is online, but it's very difficult to find specific information
• sidewalks
  • typical sidewalk dimensions:
    
• Typical parking space dimensions, by US laws: "8.5 by 18 feet".  That's around 2.59 by 5.48 meters.