Sustainability of Digital Formats: Planning for Library of Congress Collections
Sustainability of Digital Formats: Planning for Library of Congress Collections |
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| Introduction | Sustainability Factors | Content Categories | Format Descriptions | Contact | |
| Full name | Arc Digitized Raster Graphic (ADRG) |
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| Description |
ADRG is a standard National Imagery and Mapping Agency (NIMA) digital product designed in 1989-90 to support applications that require a raster map background display. ARC Digitized Raster Graphics (ADRG) are digitized maps and charts transformed into a specific georegistration framework and accompanied by ASCII encoded support files. Maps/charts are converted into digital data by raster scanning and transforming and georeferencing the map image using the equal arc-second raster chart/map (ARC) system in which the globe is divided into 18 latitudinal bands or zones. The source graphic is normally a map sheet. Data collected from a single chart/map series and scale can be maintained as a worldwide seamless data base of raster graphic data with each pixel having a distinct geographic location. ADRG is a military format that conforms to the ISO 8211 standard for an ASCII data description followed by binary image data. The intended exchange medium for ADRG is a compact disk (CD-ROM). For distribution, ADRG data is divided into geographic data sets referred to as Distribution Rectangles (DRs). One or more DRs fit onto a single CD-ROM. One or more source graphics are placed into each DR. ADRG data files are arranged hierarchically. The top level contains information relevant to the entire CD-ROM volume, the second level contains DR related files, and the bottom level contains source graphic related files. Each ADRG volume contains a header file, TRANSH01.THF, and a color test patch image file, TESTPA01.CPH. There will also be one or more DR subdirectories. Each subdirectory contains a general information file, (*.GEN), a quality file (*.QAL), and a reduced resolution overview image file (*.OVR), There will be one or more ADRG image files (*.IMG) and one or more source graphic subdirectories. Each source graphic subdirectory contains a source graphic information file (*.SOU) and zero or more legend image files (*.LGG). |
| Production phase | ADRG is a middle-state or final-state format, a general-purpose raster dataset for map displays on mission planning systems, Command and Control systems, and aircraft cockpits. |
| Relationship to other formats | |
| Contains | ISO_8211, ISO/IEC 8211 Data Descriptive File (DDF) |
| Contains | BSQ_enc, Band Sequential (BSQ) Image Encoding. See page 34 of ADRG specification. Document available through Internet Archive. |
| Has later version | Compressed ARC Digitized Raster Graphics (CADRG), a format intended as a successor, not described separately at this site. |
| LC experience or existing holdings | |
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| LC preference |
| Disclosure | Military standard, openly documented. Unclassified. |
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| Documentation | Military Specification: Arc Digitized Raster Graphics (ADRG), MIL-A-89007 22 Feb, 1990. Document available through Internet Archive. |
| Adoption |
Within U.S. Department of Defense, ADRG supported the Navy's AV8B program and the Army's Maneuver Control System. Products produced in ADRG include:
MIL-A-89007 states ADRG is inactive for new design, and is no longer used, except to support existing systems. The corresponding performance specification to be used in new system design is MIL-PRF-89038, Compressed Arc Digitized Raster Graphics (CADRG), dated 6 October 1994. However, in their 2004 paper, Managing Large Collections of NGA Raster Data, Traphan & Bauch argue that CADRG turns out to be a poor substitute for ADRG for many purposes. They describe how, of the 10,750 ADRG products currently available, 5,052 of them have been issued since the notice of inactivation. |
| Licensing and patents | None |
| Transparency | This format ranks highly for transparency. The underlying images in Band Sequential Encoding can be rendered by other tools. Support files are in ASCII. |
| Self-documentation | The format includes structural and descriptive metadata in ASCII support files. |
| External dependencies | None |
| Technical protection considerations | There is a Security and Release field used to define the security classification of the source graphic (T=Top Secret, S=Secret, C=Confidential, R= Restricted, and U=Unclassifiied) and an accompanying date (if any) of classification downgrading. |
| Still Image | |
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| Normal rendering | The format is designed to support on-demand mosaicing of images at a particular scale through retrieval of small tiles. Support for zooming was not part of the design and is limited. |
| Clarity (high image resolution) | Bit-depth limited to 24 bits, for red, green, and blue color bands. Spatial resolution capabilities intended to be adequate to support screen display. In original production process, scanning was at 250 lines per inch. Images are organized as "distribution rectangles" in 128x128 pixel tiles; the size of distribution rectangles is constrained by the physical media (typically CD-ROM). |
| Color maintenance | ADRG images are in band sequential form with red, green, and blue bands. The test patch image portrays a set of standard colors, which may be used to adjust a video monitor for more accurate color viewing of the ADRG map images. |
| Support for vector graphics, including graphic effects and typography | No support for vector graphics. |
| Support for multispectral bands | ADRG images have a Band_ID_Field that documents the band color and lower and upperband edge wavelengths in nanometers. |
| Functionality beyond normal rendering | The ADRG format and process is designed to permit a worldwide seamless dataset for map data of a given scale. |
| GIS images and datasets | |
| Normal functionality | Each source graphic is described by a source file (.SOU), which provides various ancillary data values describing the source graphic. This includes such items as source graphic classification, geographic boundary, and datum. The ARC system provides a rectangular coordinate and projection system at any scale for the entire ellipsoid based on the World Geodetic System 1984 (WGS 84). (Link available through Internet Archive.) |
| Support for GIS metadata | Polynomial coefficients and parameters are computed for each source graphic to support projection space computations from source datum and source coordinates to WGS84. These coefficients and parameters are called Metric Support Data (MSD) and are recorded in the .SOU file. The process and parameters are documented in Appendix section 30 (page 38) of Military Specification: Arc Digitized Raster Graphics (ADRG) (MIL-A-89007). (Document available through Internet Archive.) |
| Support for grids | Not applicable to digitized paper maps or charts. |
| Beyond normal functionality | Quality data consists of the horizontal and vertical accuracies (absolute and relative) for a DR. Accuracies are given for one or more subregions, each of which is defined by a set of geographic coordinates. The quality data is contained in the file *.QAL. Legend images are rectangular patches scanned from the margin of the source graphic. A legend image is designed to capture data not easily captured as text. Legend data is unique to the source graphic. See MIL-A-89007 (Appendix section 40) for more detail regarding predefined legends, which include diagrams, glossaries, and landmark features symbols. (Document available through Internet Archive.) |
| Tag | Value | Note |
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| Filename extension | thf cph gen qal ovr img sou lgg |
An ADRG dataset is made of several files, including the Transmittal Header File (.THF), Test Patch Image file (.CPH), General Information File (.GEN), Quality File (.QAL), the overview image file (.OVR), the image files (.IMG), the Source file (.SOU), and the Legend Image file (.LGG). |
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| History |
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