1. Topological Vector Profile (TVP), SDTS Part 4

Intended Use --

The TVP is designed to transfer digital geospatial vector data that conforms to a planar graph and has both "chain to node" and "chain to area" topological relationships. Chains, nodes, points, areas, and composite objects are the primary components. Census TIGER data and USGS DLG data can use the TVP. The TVP can accommodate both feature-based and non-feature-based data. Feature-based information, using SDTS composite objects, can be nonplanar even though the spatial primitives are planar, and can support many-to-many relationships between features and location primitives.

Primary Sponsors, Interested Groups, and Contacts --

USGS is now using the TVP for on-line distribution of all DLG data. FWS has sample National Wetland Inventory data in TVP. Census has sample TIGER data in TVP and may use the TVP for Framework boundary data. FEMA plans to put flood boundary data into the TVP. BLM plans to put land management data into the TVP as one option within the new Cadastral Data Standard. Other federal and state agencies are investigating use of this profile for their vector data.

Contact the SDTS task force via e-mail at

sdts@usgs.gov

Additional information is available on-line at the SDTS web site

http://mcmcweb.er.usgs.gov/sdts

Documents --

The TVP exists as a documented part (Part 4) of FIPS 173-1 (SDTS). Version 1 .0 of the TVP dated June 10, 1994 is now out of print. A draft ANSI version of the TVP, dated December 13, 1995, with minor editorial changes is available at the SDTS web site

http://mcmcweb.er.usgs.gov/sdts

Preparation of TVP and other SDTS documents for ANSI review and approval is now underway by private contract.

Additional documents, that describe the specific product mappings to SDTS-TVP from TIGER, DLG-3, and DLG-F, are also available at the SDTS web site.

Several articles on SDTS and the TVP have been in GIS-related journals includ ing "Understanding SDTS Topological Vector Profile Implementation" by Bob Lazar in the June 1996 issue of Geo Info Systems. The ESRI White Paper "SDTS-Supporting the Spatial Data Transfer Standard in ARC/INFO" is available at

ftp://ftp.esri.com/pub/marketing/white_papers/sdts.pdf

Software --

Software that supports the TVP is part of the suite of SDTS++ public-domain t ools for access and interface to SDTS. Contact the SDTS task force (sdts@usgs.gov) or check the SDTS web site for details.

Translators --

TVP translators are supported by ESRI (Arc/INFO 7.04 and above), Intergraph ( MGE), GRASS, ERDAS (using ESRI translator), and AST GeoMorph; are planned by MapInfo, UNISYS , SAFE FME, Laser-Scan (for South Korea), and LAS GrassLand; and are being considered by Applied Geographics, Autodesk, and SmallWorld based on customer demand.

Data --

Sample TIGER, DLG, and NWI data is available in SDTS-TVP. Nationwide USGS 2- million, 100K, and 24K DLG-3 transportation, hydrography, PLSS, and boundaries data is now available in the TVP.

Conformance Testing --

A beta series of conformance testing involving NIST, USGS, Intergraph, and ADC was conducted in 1996. Official conformance testing will begin in the near future through private contractors.

With the large volume of DLG-3 data now in SDTS, the temptation may be to develop SDTS-TVP translators that are based on DLG-3 content specifications. This limits the utility of the translator and should be discouraged. Conformance testing of translators should help avoid this problem. A good SDTS-TVP translator should be content independent and product independent so that it accommodate SDTS-TVP data not just from USGS, but from Census, BLM, and others.

Future Plans --

ANSI and ISO approval for the TVP (SDTS Part 4), along with Parts 1, 2, 3, 5, & 6 of SDTS, will be sought. Development and approval of conformance testing tools and procedures will soon be moved to the private sector. More USGS data in SDTS-TVP will become available as a regular part of the production process. SDTS will be the standard distribution format for USGS-NMD digital geospatial data products. An on-line help desk at sdts@usgs.gov is now in place, and better tools and experience with TVP translators are being investigated.