Road Data Representation
From Road Name Data Wiki
Contents |
Road Corridors & Road Parcels
The property model proposes a fully tiled property layer where the entire layer is covered in a mosaic of corridor and property polygons. In some instances the polygons will overlap, for example, a private road across a property. There should be no areas that are not covered by a either a corridor or property.
The road corridors will comprise the parcels that have been vested in the relevant road authority; for municipal public roads this is council. The sum of parcels forms the road corridor. Road carriageways will lie within the road reserve these may or may not be modelled as carriageway polygons. The road reserve should abut the properties.
The development of road polygons will require collaboration with Vicmap to identify the parcels and the Office of Titles to ensure completeness.
Road Classification Hierarchies
There is a fixation amongst asset managers and engineers with finding that single roads classification hierarchy that will serve all events. The ICSM recently undertook a research project into road classification hierarchies applied by mapping and road traffic authorities throughout Australia and internationally.
The research highlighted that:
“… no single classification appears to be perfectly applicable. Rather, they all exhibit certain flaws and beneficial elements with respect to fundamental classification characteristics.”[1]
The harder one looks the more elusive a single hierarchy becomes. As governments are moving from functional, project based, models of road management towards outcome, service oriented approaches[2]; there is a realisation that the outcomes are not delivered by individual road components but by the network as a whole. There is no value in getting a double B truck from Mildura to Frankston if the vehicle can’t access the depot. It is the collective network of roads that ultimately delivers the primary service of accessing and linking places. However, this same road network enables many other services outcomes, such as location addressing. These road networks are collectively managed by multiple organisations and increasingly incorporate local communities in decision making regarding the outcomes they want from the network. They have very different usage profiles that don’t necessarily correlate with their function. As a result their form is no guarantee of their primary function within the network.
Across the road network there’s a multitude of organisations, functions, forms and service roles that form a complex web of relationships that have to be managed. These relationships are best described as a network or web, they are not a hierarchy. Attempts to assemble them in a hierarchical taxonomy based on say, form, usage or function appear to trip up when the service outcomes are laid over the top. The result is a very deep decision tree classification that is cumbersome to work with or a compromised structure that is “generally” right.
The approach put forward by the working groups is to allow multiple classification hierarchies that each serve a tightly defined purpose. In particular, the proposal separates road form from road function and provides separate hierarchies for road administration, accessibility and addressing.
At the time of writing this paper the ICSM have not formed a conclusive view on road hierarchies. However, their report strongly leans towards the PSMA classification system:
“This research also indicated that the PSMA classification has, above all other existing Australian road classifications, the potential to be applied as the national model. However, the research did identify several considerations that could improve the PSMA model, that warrant further investigation.”1
Using an overloaded classification system is likely to provide limited benefit, especially as we move towards a service outcome driven investment and management frameworks for roads.
Linear Referencing
During the workshops several Council GIS officers made strong representation that the data models for road attributes and linear features should be based on a linear reference system rather than a segment system. The belief was that a linear reference model would provide a more robust framework to manage future changes to the road attributes. For example; if the seal type changes under the segment model it requires a new segment for all attributes, whilst under a linear reference framework the change is confined to the linear reference for the seal.
The current Vicmap Transport model is based upon a segment model.
The ICSM have formed a Roads Working Group (ICSM - RWG), which is examining the requirements for a roads data framework. They are currently looking closely at EuroRoads , the European framework for roads data, which uses a linear referencing framework. The USA government geographic framework also adopted a linear reference model.
A move from the current segment framework to a linear referencing framework represents a significant shift and needs to be managed systematically and co-ordinated with the ICSM RWG future direction to avoid councils making investments in a “technology cul de sac.”
Data Accuracy
Data Alignments
As part of councils asset management program many of the municipal public roads are physically assessed to generate inventory and condition reports. Increasingly more and more councils are incorporating GPS data collection in this process. As the positional accuracy of GPS units continues to improve many councils are developing (or have the potential to develop) a comprehensive digital survey model of their road network.
The issue raised in the workshops was how to manage the digital road alignment with that provided by Vicmap Transport and linked to Vicmap Property. Councils noted that whilst they have the capacity to mark up the GPS digital survey, they were not in a position to synchronise the changes with the parcel and property layers.
As part of the next phase of work the MAV in partnership with DSE will be required to develop a standard for the digital survey of roads to be used in conjunction with the asset management condition and inventory data collection.
Data Accuracy
The Vicmap Transport Product Specification discusses the historical and future requirements for data accuracy. A detail discussion and formal proposal regarding the level of survey accuracy required by local government is believed to be a necessary component of the data custodianship arrangements. It is recommended that the MAV and DSE establish a joint working party that collaborates with local government asset managers and planners to develop a road alignment data accuracy policy and strategy. Spatial Reference Systems The foundation for all spatial information is the geodetic control network, upon which all other data is based. Geodetic Control is the fundamental basis of all Victorian spatial infrastructure, including all other framework information data sets. The preferred datums and projection under VSIS are : • Geocentric Datum of Australia – 1994 Adjustment (GDA94) • Australian Height Datum (AHD) …. unchanged by the move to GDA, and • Degrees and decimals of a degree - GDA94 latitude/longitude, or • Easting and Northings in metres - MGA94 Zone 54 or Zone 55 or VICGRID94.
Navigation
- Road Definitions
- Data Attributes
- Road Data Representation
- Data Dictionary
- Domain Model.
References
- ↑ RWG for the ICSM, October 2006, “Assessing the Feasibility of a National Road Classification, Report to ICSM on National Road Classification Developments,” www.icsm.gov.au accessed on 17th April 2008
- ↑ Gary Liddle, CEO, VicRoads, April 10, 2008, VicRoads Strategic Focus. 2008 National Local Government Asset Management and Public Works Engineering Conference, Telstra Dome, Docklands, Melbourne, Keynote presentation: VicRoads’ future directions including the transition form a “project-based focus” to an “outcome-based model” and is seeking partnering arrangements with local governments to identify the main road priorities as part of a holistic approach, focusing on outcomes for road users.
