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Implementing SDTS through Profiles

The Spatial Data Transfer Standard (SDTS) is implemented through the use of profiles. Since the SDTS is designed to support all types of spatial data, implementing all of the standard's options at one time would be a monumental task. Profiles provide the best method for successful implementation of SDTS. Profiles balance two objectives of SDTS, first to allow both encoding and decoding to be feasible, and second to ensure that all meaningful information is transferred.

Profiles balance two objectives of SDTS, first to allow both encoding and decoding to be feasible, and second to ensure that all meaningful information is transferred.

A profile is intended to provide specific rules for applying SDTS base specifications (Part 1, 2, and 3) to a particular type of spatial data. A profile can be considered a subset of the SDTS specification that defines:

o Restrictions and requirements for use of specific spatial object types

o Restrictions and requirements for use of SDTS modules, including rules for choosing among options present in the base specifications

o Module naming and file naming conventions

o Use of ISO 8211 encoding specifications, including allowable options

As the SDTS concerns itself with all spatial data types and their variations, a profile is created to handle a particular model of spatial data. Profiles are designed with enough flexibility to account for variability in user data models, thus avoiding l arge proliferation of profiles for different data models that are similar in structure. Several user data formats and data products can share a single profile. For example, the Topological Vector Profile will handle USGS DLG, Census TIGER, ESRI Coverage, and any other topologically structured vector data set.

All SDTS transfers must be encoded under a profile. Users of the SDTS are encouraged to make every effort to conform to an existing profile. The existence of many competing or conflicting profiles to SDTS would require a large number of translators and this defeats the goal of having a common transfer standard to spatial data.

Specific SDTS Profiles

Topological Vector Profile (TVP). The TVP is endorsed by FGDC as FGDC-STD 002.4. It is the first completed and NIST approved profile and is included as Part 4 of the SDTS. The TVP was developed to support geographic vector data with geometry and topology. It includes the SDTS defined spatial objects representing vector data with full topology that comprise a two-dimensional manifold. Data sets may contain point, line, polygon, and composite features. The TVP accommodates USGS vector products such as the Digital Line Graph (DLG) data. The Bureau of the Census will also be using the TVP to distribute its Topologically Integrated Geographic Encoding and Referencing (TIGER) data files.

Raster Profile and Extensions (RPE). (Download the free Adobe Reader) The RPE, formerly known as SRPE, is Part 5 of the SDTS. FGDC endorsed the RPE as FGDC-STD-002.5-1999. The RPE was developed to support two-dimensional spatial data sets in which features or images are represented in raster or gridded form. This profile can accommodate image data, digital terrain models, gridded GIS la yers, and other gridded data. This profile does not permit vector objects, raster objects higher than two-dimensional, or irregular grids. The RPE will accommodate USGS raster products such as Digital Elevation Models (DEM), and Digital Orthophoto Quadrangles (DOQ) data files. The Extensions support optional use of (1) the ISO Basic Image Interchange Format (BIFF) for images, (2) the JPEG File Interchange Format (JFIF) for compressed images, and (3) Georeferenced Tagged Information File Format (GeoTIFF).

Transportation Network Profile (TNP). The TNP has been prepared in draft form by the Volpe National Transportation Systems Center for the US Department of Transportation (USDOT) Bureau of Transportation Statistics (BTS). The TNP contains specifications for an SDTS profile for use with geographic vector data with network topology. Data sets are represented by vector objects which comprise a network (sometimes non-planar) or planar graph. Excluded are raster data and geometry-only vector data. Once available, the TNP will accommodate the USDOT BTS transportation network data files.

Point Profile. The Point Profile has also been referred to as the Geodetic Profile, the High Precision Point Profile, and SDTS Part 6. A draft version of the Point Profile was prepared in mid 1996 by the National Oceanic and Atmospheric Administration - National Geophysical Data Center (NOAA-NGDC) and the USGS. This profile is designed to support a major release of geodetic control point data from NOAA's National Geodetic Survey (NGS), as well as point-only data from other agencies. The adoption of this profile as an FGDC standard was sponsored by the Federal Geodetic Control Subcommittee (FGCS) of FGDC through the Standards Working Group of FGDC. FGDC approval for the Point Profile, known as FGDC-STD-002.6, was approved in 1998.

Computer Aided Design and Drafting Pr ofile (CADD). (Download the free Adobe Reader) The Computer Aided Design and Drafting Profile (CADD) contains specifications for an SDTS profile for use with vector-based geographic data as represented in CADD software. The purpose of this profile is to facilitate the transl ation of this data between CADD packages without loss of data, and support the translation of this data between CADD and mainstr eam GIS packages. CADD software makes up a large portion of the Geographic Information Systems (GIS) marketplace. CADD software allows for several types of elements, in particular, the use of three-dimensional elements and complex curves that are not comm only used by GIS. This profile allows the representation of two- and three-dimensional geographic vector data from CADD package s to be transferred via the SDTS standard. This profile supports two-dimensional vector data and three-dimensional vector data, where the third dimension is the "height" of the object. These data may or may not have topology. This profile does not suppor t raster data or two-dimensional transfers already represented by another profile. The CADD profile, approved by the FGDC in Mar ch 2000, is known as FGDC-STD-002.7-2000.

Steps for the Development and Approval of an SDTS Profile

1. Have interest in putting data into SDTS.
2. Try to match your data model to existing profiles.
3. Determine that no current profile will do.
4. Contact FGDC or SDTS authority with idea for new profile.
5. Announce intentions. Seek groups with similar needs.
6. Write new profile document using most similar profile as guide.
7. Contact NIST, FGDC SWG, ANSI, or other standards group to begin formal review and approval process , if desired.
8. Develop documents describing mappings of specific products into this profile.
9. Develop sample data sets using profile.
10. Seek vendor support for translator development.
11. Work with NIST on conformance testing.
12. Begin producing or exchanging data using profile.

red ballTo view Parts 1 - 5 of SDTS
red ballTo view the draft Transportation Network Profile document
red ballTo see an HTML version of the draft Point Profile document

red ballFor a detailed overview of SDTS Profiles
red ballFor more informative articles on Profiles visit our SDTS Information FTP Site
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