DIGEST Overview
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  • DIGEST Overview
  • Components of DIGEST
  • Changes from the Last Edition

    [DIGEST Overview]

    The Digital Geographic Information Exchange Standard (DIGEST) was developed by the Digital Geographic Information Working Group (DGIWG) to support efficient exchange of Digital Geographic Information among nations, data producers, and data users.

    Authority. The DIgital Geographic Information Exchange STandard (DIGEST) was prepared by and issued under the authority of the Digital Geographic Information Working Group (DGIWG).

    Security Classification. All parts of DIGEST are unclassified but may be subject to the limitation of use that the copying of the documents is prohibited without the authority of the national representative (see Part 1 Clause 5.2).

    Digital Geographic Information Working Group (DGIWG). DGIWG was formed to develop standards to support the exchange of Digital Geographic Information (DGI) among NATO nations. Interoperability and burden sharing continue to be the goals of the DGIWG since the group's establishment in 1983. Many of the DGIWG standardization achievements have been adopted directly by NATO. The current DGIWG membership and work program extends beyond NATO.

    Implementation. Since the early 1990's, the DGIWG has maintained and extended DIGEST to satisfy the current and emerging needs of the DGIWG community. Over the years, DIGEST has become the basis for co-production opportunities between nations. DIGEST-compliant datasets are being produced and exchanged by numerous nations to support a variety of military and civilian applications. DIGEST is NATO Standardization Agreement (STANAG) 7074.

    DIGEST Components and Document Structure. DIGEST is a comprehensive "family of standards" capable of supporting the exchange of raster, matrix, and vector data (and associated text) among producers and users. DIGEST can support the entire range of levels of topological structures.

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    [Components of DIGEST]

    DIGEST is divided in 4 parts:

    • Part 1 consists of a brief General Description of the standard.

    • Part 2 consists of the Theoretical Model, Exchange Structure, Encapsulation Specifications (Annexes A through D) and a Standard ASCII Table of Contents (Annex E).   The Part 2 encapsulations include:

    • Annex A – based on ISO 8211 – Information Processing - Specification for a descriptive file for information interchange.

    • Annex B – based on ISO 8824 – Information Processing Systems – Open Systems Interconnection – Specifications of Abstract Syntax Notation One; and ISO 8825 – Information Processing Systems – Open Systems Interconnection – Specification of Basic Encoding Rules for Abstract Syntax Notation One.

    • Annex C – Vector Relational Format (VRF) Encapsulation Specifications – "Table-based direct-use format" for vector data.

    • Annex D – Image Interchange Format (IIF) Encapsulation Specifications – based on the NATO Secondary Imagery Format (NSIF) profile of ISO 12087-5 - Basic Imagery Interchange Format (BIIF).

    • Part 3 consists of Codes and Parameters.

    • Part 4 is the Feature Attribute Coding Catalogue (FACC) Data Dictionary – FACC is a comprehensive coding scheme for features, feature attributes, and attribute values.

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    [Changes from the Last Edition]

    DIGEST Edition 2.1 cancels and replaces DIGEST Edition 2.0 (June 1997). The major changes are documented below:

    Changes:   Incorporation of corrections and clarifications accumulated since version 2.0.

    Part 1:

    • Revision of the general description of DIGEST to reflect an emphasis on standardizing geographic information content that may be exchanged using different encapsulations or stored in data bases or data warehouses.

    • An indication in the general description of DIGEST of the increased level of alignment between DIGEST and other external standards, in particular, the International Hydrographic Organization S-57 standard, the ISO / TC211 suite of Geographic Information / Geomatics standards and the ISO JTC1 SC24 Image Processing Standards.

    Part 2:

    • Addition of circular arcs as a geometric primitive. (Annex C, C.

    • Addition of an optional z attribute parameter for geometric primitives, which provides a method of storing multiple z-values in select cases where disjoint z-values occur. (Annex C, C.

    • The use of the z attribute parameter in coordinates for geometric primitives to represent the elevation (special cases) at the location in a 2.5-D context. That is two-dimensional planar graph topology applies on a manifold in three dimensions. (The special cases and limitations have been defined for Annex C.)

    • Extension of feature relations (i.e., stack-on/stack-under), previously limited to the coverage level and the library level. (Annex C, C.

    • Addition of optional columns in the feature join table to support the storage of source information down to the feature and attribute level. (Annex C, C.

    • Defined standardized coded values commonly associated with attribute values (i.e., null, unknown). Provides encoding mechanism for non-coded attribute types. (Annex C, C.

    • Revision of DIGEST Part 2 Annex D "Image Interchange Format (IIF) Encapsulation Specification", to bring it into full alignment with the current editions of the NATO Secondary Imagery Format STANAG 4545 Edition 1 Amendment 1, the ISO 12087-5 Basic Image Interchange Format (BIIF) and the US National Imagery Transmission Format (NITF), MIL-STD 2500B Change Notice 1 and 2.

    • Replacement of Annex E with enhanced capabilities to support exchange of DIGEST information packages together with non-DIGEST set of files.

    • Clarification of the use of Not A Number (NAN) and special case enumerated values.

    Part 3:

    • Revision of Clause 5 to more clearly define the basic numerical primitives used in Part 2 Annex E and to clearly specify the Not A Number (NAN) values.

    • Revision of Clause 6 to update geodetic codes and parameters.

    Part 4:

    • Deletion of attribute and feature language translations from published version. (Translations on Internet page.)

    • Harmonization of DIGEST FACC Data Dictionary with the IHO S-57 Object Catalogue.

    • Enhanced explanations of concepts and implementation issues.

    • Backward compatibility documentation.

    Acknowledgement. The editor would like to acknowledge the efforts and contributions of all DGIWG members—past and present—in the creation and evolution of this standard.

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