5. Transportation Profile(s)

Including:

(1) current Transportation Network Profile (TNP),

(2) proposed complete transportation transfer profile,

(3) proposed ITS profile with subprofiles.

Intended Use --

The current and proposed transportation profiles to SDTS are all designed to transfer and archive digital geospatial data about transportation networks (e.g., roadways, railways, navigable waterways, transit systems), transportation facilities, and related events and features.

(1) TNP --

The TNP is designed to allow the seamless representation of overpassing roadways using spatial primitives that need not be broken at overpasses and underpasses. To accommodate this, TNP data is not limited to a planar graph at the basic geometry element level. "Chain to node" relationships are the only required topological relationships between spatial primitives. Areas are not required. The primary SDTS objects are network chains, nodes, and composite objects (used for routes).

Some sample railway data in SDTS-TNP is available. Future use of the TNP by the US DOT for data distribution and data exchange will be considered after reconciliation of the TNP with the proposed SDTS ITS (GDF) profile, and reconciliation with the a proposed transportation profile to SDTS that supports linear referencing and is based on a complete enterprise GIS-T data model.

(2) Complete Transportation Profile --

The proposed, more complete, transportation transfer profile to SDTS will be based on an enterprise GIS-T data model from the recent work of Ken Dueker and Al Butler (1997). One aspect of this profile is more support for the linear location referencing of both tangible objects and characteristics from the earlier LRS data model research coordinated by Alan Vonderohe and refined in the ISTEA Pooled Fund work of David Fletcher and associates. For transportation data, SDTS needs to "provide an attribute-centric way to transfer transportation system characteristics independently of cartography" [from Dueker & Butler, 1997].

The enterprise GIS-T model supports multiple, independent cartographic representations, e.g., bridge geometry as points or point events at low resolution and as strings or linear events at high resolution. It supports variable linear feature segmentation as an alternative to rigid segmentation. New or modified SDTS terms are included, with a greater distincti on between (i) geographic or real-world references and locations and (ii) cartographic references and locations for map related CAD and GIS graphic elements. New linear datum objects include anchor points, anchor sections, and reference points. The use of a "transportation feature" with a permanent, unique identifier within a jurisdiction is included. There is advanced support for names. Junctions can be subtyped as intersections, interchanges, overpasses, intermodal connections, and intersections with boundaries; and they can be related to points at small scales and strings or interchange drawings at large scales. These junctions can be linked to information for traffic control, turn possibilities, overpass loads, and underpass clearances. The Dueker/Butler model also provides support street addresses as a for of linear referencing.

(3) ITS Profile --

An Intelligent Transportation Systems (ITS) profile to SDTS, or a Graphic Dat a Files (GDF) profile to SDTS, has been proposed by the ITS community in the U.S. (ITS America, NavTech, ETAK, AAA, Ford, Oak Ridge, SAE, etc.). The ITS profile to SDTS will probably be based on GDF, but there is a small chance that it could be non-GDF.

"What is GDF?

"GDF Geographic Data Files is a European [CEN] standard, that is used to describe and transfer road networks and road related data. It is much more than a generic GIS standard, because GDF gives rules how to capture the data, how the features, attributes, and relations have been defined.

"... It's primary use will be for car navigation systems (Bosch, Philps, Volvo, etc.), but it is very usable for many other transport and traffic applications..."

[From http://www.ingr.com/ehq/gdf]

GDF (CEN, 1995) uses a feature-based model, similar to DIGEST/VPF and USGS DLG-F (Hickman, 1995). This allows use of a topologically structured planar graph at the primitive geometry level, while supporting nonplanar transportation network components (seamless, overpassing road segments) at the simple feature level. GDF also supports multi-scale feature representations, and explicit relationships between features. ISO TC 204 WG 3 subgroup 3.1 is working on an international map database transfer standard for ITS based on an ISO update of GDF from CEN TC 278. The ISO version of GDF should be available in 1998. GDF uses ISO 8211 at the physical implementation level, similar to SDTS and DIGEST.

GDF provides some basic support for linear location referencing. Attributes in GDF are associated with a "feature in such a way that they reference a certain part of it. These attributes are called 'Segmented Attributes.' With line features, the part which is referenced by the segmented attributed is defined by a 'position from' and a 'position to' value. These positions represent the curvimetric distance" [from 1992 GDF Attribute Catalogue]. Curvimetric distance is based on the representational geometry, which may not be as robust as the linear location referencing used in the other transportation profile proposed by Dueker and Butler. Version 3.0 of GDF (CEN, 1995) accommodates addresses in section 5.2.10 (Address Area).

In a 1994 meeting, the IVHS America (now ITS America) Standards and Protocols Subcommittee on Map Databases and Information Systems developed requirements for a GDF profile to SDTS. These requirements included possible specific subprofiles based on ITS business areas, including Advanced Public Transportation Systems (APTS) (Watje & Okunieff, 1995), Commercial Vehicle Operations (CVO), and Advanced Vehicle Control Systems (AVCS). The APTS subprofile to SDTS was also suggested as a transit subprofile to the TNP.

Primary Sponsors, Interested Groups, and Contacts --

(1) The FGDC Ground Transportation Subcommittee (GTS) and the US DOT Bureau of Transportation Statistics (BTS) were the primary sponsors of the TNP, with development work done at the Volpe National Transportation Systems Center. Additional information is available on-line at the BTS web site

http://www.bts.gov/

or the FGDC Ground Transportation Subcommittee (GTS) web site

http://www.bts.gov/programs/gis/fgdc/fgdc.html

The FGDC GTS is also very interested in GDF-based transfer standard with more linear location referencing support.

(2) Prof. Ken Dueker at Portland State University and Al Butler from Florida have recommended the complete transportation profile based on an enterprise GIS-T data model. E- mail for this issue can be sent to Al Butler at abutler@nettally.com

(3) ITS America, Oak Ridge National Labs, and Viggen Corp. are involved with the ITS profile.

Documents --

(1) Requirements for the TNP have been documented. Version 1.1 of the TNP is dated February 1, 1996 and is available at the BTS or FGDC GTS web sites

(2) The 1997 document "GIS-T Enterprise Data Model with Suggested Implementation Choices" by Dueker and Butler is available at

http://www.upa.pdx.edu/CUS/

and includes SDTS recommendations for transportation in Appendix 5.

(3) Requirements for an ITS profile were developed by ITS America's Standards and Protocols Subcommittee for Map Database and Information Systems in 1994. More GDF-specific information is available at

http://www.intergraph.com/ehq/gdf/index.htm

Software --

SDTS TNP Encoding Software has been developed at the US DOT Volpe National Transportation Systems Center, Cambridge, Massachusetts. Information is available at the FGDC GTS web site. SDTS TNP, as well as SDTS TVP, are supported by the GeoMorph conversion tool developed by Application Software Technologies, Inc.

Future Plans --

GDF, along with SDTS, DIGEST, and similar exchange standards have been suggested as ISO standards (see later section on ISO harmonization). Some reconciliation among standards may be required by ISO. The proposed ITS (GDF) profile to SDTS fits into this harmonization effort. SDTS is a configurable standard so it can be made to accommodate the models of other standards such as the feature-based models of GDF and DIGEST/VPF. Because of the configurable nature and model independence of SDTS, it has been recommended as a "harmonizing agent" or "umbrella" for other standards. DIGEST should also be considered in this transportation discussion because it is now designated as a civilian transportation standard in Canada and as a general standard by the defense communities of many nations.

The requirements and possibilities for one or two new transportation profiles to SDTS need to be clarified and documented. Some of the overlapping possibilities may include the following.

(a) Wait for several possible developments. Wait, watch, and react to further standards developments at the ISO level among SDTS, GDF, and DIGEST/VPF (discussed later). Wait for further SDTS developments, e.g., a more inclusive object-based profile (discussed later) which may be related to an archive standard for OpenGIS. Wait for further momentum or requirements from FGDC, e.g., for framework distribution and archive. Wait for further requirements and demand from major data producers and GIS vendors. Wait for sufficient user dissatisfaction with current use of format translators for spatial data exchange. Use SDTS-TVP (see D. Schmidt 1997 thesis) for transportation data exchange while waiting.

(b) Replace or modify the TNP into two transportation standards; a GDF profile to SDTS to accommodate the ITS community and an enterprise GIS-T profile. Doing GDF, GIS-T, and SDTS all at once may (or may not) be too large an initial task. An ITS profile may be a first step, with the intention to include GIS-T and LRS requirements as a second step after learning from the first step.

(c) Define an overall architecture or approach (Butler, 1997 correspondence), then develop a single, combined GIS-T and GDF-based ITS profile to SDTS as "THE Transportation Profile to SDTS." This will help avoid rendering any initial components obsolete.

(d) Work with developers of a proposed object-based profile to SDTS and with the new OGC (OpenGIS) Transportation Domain Technical Working Group to include complete transportation and GDF requirements in the object-based profile.

There are various pros and cons for each of these possibilities. Some transportation specific presentations and discussions are planned for an SDTS workshop in September, 1997. This document should be updated after those meetings.