Raster Product Format

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Raster Product Format (RPF), from NGA, is primarily used for military purposes by defense contractors. RPF data are organized in 1536 × 1536 frames, with an internal tile size of 256 × 256 pixels. RPF data are stored in an 8-bit format, with or without a pseudocolor lookup table.

RPF Data are projected to the ARC system, based on the World Geodetic System 1984 (WGS 84). The ARC System divides the surface of the ellipsoid into 18 latitudinal bands called zones. Zones 1-9 cover the Northern hemisphere and zones A-J cover the Southern hemisphere. Zone 9 is the North Polar region. Zone J is the South Polar region.

Polar data is projected to the Azimuthal Equidistant projection. In nonpolar zones, data is in the Equirectangular projection, which is proportional to latitude and longitude. ERDAS IMAGINE includes the option to use either Equirectangular or Geographic coordinates for nonpolar RPF data. The aspect ratio of projected RPF data is nearly 1; frames appear to be square, and measurement is possible. Unprojected RPFs seldom have an aspect of ratio of 1, but may be easier to combine with other data in Geographic coordinates.

Two military products are currently based upon the general RPF specification:

  • Controlled Image Base (CIB)
  • Compressed ADRG (CADRG)

Raster Product Format is described in military specification MIL-STD-2411 (2), published by National Geospatial-Intelligence Agency.

RPF employs Vector Quantization (VQ) to compress the frames. A vector is a 4 × 4 tile of 8-bit pixel values. VQ evaluates all of the vectors within the image, and reduces each vector into a single 12-bit lookup value. Since only 4096 unique vector values are possible, VQ is lossy, but the space savings are substantial. Most of the processing effort of VQ is incurred in the compression stage, permitting fast decompression by users of data in the field.

RPF data are stored with the following structure:

  • Root contains an RPF directory. This RPF directory is often referred to as the root of the product.
  • RPF directory contains a table-of-contents file, named A.TOC, which describes the location of all of the frames in the product.
  • RPF directory contains one or more subdirectories containing RPF frame files. RPF frame file names typically encode the map zone and location of the frame within the map series.
  • Overview images may appear at various points in the directory tree. Overview images illustrate the location of a set of frames with respect to political and geographic boundaries. Overview images typically have an .OVx file extension, such as .OVR or .OV1.

All RPF frames, overview images, and table-of-contents files are physically formatted within an NITF message. Since an RPF image is broken up into several NITF messages, ERDAS IMAGINE treats RPF and NITF as distinct formats.

Loading RPF Data

RPF frames may be imported or read directly. The direct read feature, included in ERDAS IMAGINE, is generally preferable since multiple frames with the same resolution can be read as a single image. Import may still be desirable if you wish to examine the metadata provided by a specific frame. ERDAS IMAGINE supplies four image types related to RPF:

  • RPF Product—combines the entire contents of an RPF directory, excluding overview images, as a single image, provided all frames are within the same ARC map zone and resolution. The RPF directory at the root is the image to be loaded.
  • RPF Frame—reads a single frame file.
  • RPF Overview—reads a single overview frame file.
  • RPF Table of Contents—reads the table-of-contents file.

CIB

Controlled Image Base (CIB) is grayscale imagery produced from rectified imagery and physically formatted and compressed to RPF Standard. CIB offers a compression ratio of 8:1 over its predecessor, ADRI. CIB is often based upon SPOT panchromatic data or reformatted ADRI data, but can be produced from other sources of imagery.

CIB format is described in Military Specification MIL-PRF-89041A.

CADRG Data

Compressed ADRG (CADRG) data consist of digital copies of NGA hard-copy graphics transformed into the ARC system. CADRG data is derived from ADRG and other digital sources through compression and reformatting to Raster Product Format (RPF) Standard. The data are scanned at a nominal collection interval of 150 microns. The resulting image is 8-bit pseudocolor, which is physically formatted as a compressed RPF.

CADRG is a successor to ADRG, Compressed Aeronautical Chart (CAC), and Compressed Raster Graphics (CRG). CADRG offers a compression ratio of 55:1 over ADRG, due to the coarser collection interval, VQ compression, and the encoding as 8-bit pseudocolor, instead of 24-bit truecolor.

CADRG format is described in Military Specification MIL-PRF-89038 (2).

ADRG Data

ADRG (ARC Digitized Raster Graphic) data was provided by National Geospatial-Intelligence Agency (NGA). ADRG format is described in Military Specification MIL-A-89007. ADRG data was primarily used for military purposes by defense contractors. The data are in 128 × 128 pixel tiled, 8-bit format. ADRG data provide large amounts of hard-copy graphic data without having to store and maintain the actual hard-copy graphics.

ADRG data consist of digital copies of NGA hard-copy graphics transformed into the ARC system and accompanied by ASCII encoded support files. These digital copies are produced by scanning each hard-copy graphic into three images: red, green, and blue. The data are scanned at a nominal collection interval of 100 microns (254 lines per inch). When these images are combined, they provide a 3-band digital representation of the original hard-copy graphic.

ARC System

ARC system (Equal Arc-Second Raster Chart/Map) provides a rectangular coordinate and projection system at any scale for the Earth’s ellipsoid, based on the World Geodetic System 1984 (WGS 84). ARC System divides the surface of the ellipsoid into 18 latitudinal bands called zones. Zones 1 - 9 cover the Northern hemisphere and zones 10 - 18 cover the Southern hemisphere. Zone 9 is the North Polar region. Zone 18 is the South Polar region.

Distribution Rectangles

For distribution, ADRG are divided into geographic data sets called Distribution Rectangles (DRs). A DR may include data from one or more source charts or maps. The boundary of a DR is a geographic rectangle that typically coincides with chart and map neatlines.

Zone Distribution Rectangles

Each DR is divided into Zone Distribution Rectangles (ZDRs). There is one ZDR for each ARC System zone covering any part of the DR. The ZDR contains all the DR data that fall within that zone’s limits. ZDRs typically overlap by 1,024 rows of pixels, which allows for easier mosaicking. Each ZDR is stored as a single raster image file (.img). Included in each image file are all raster data for a DR from a single ARC System zone, and padding pixels needed to fulfill format requirements. The padding pixels are black and have a zero value.

SHARED Tip Padding pixels are not imported by ERDAS IMAGINE, nor are they counted when figuring the pixel height and width of each image.

ADRG File Format

ADRG format contains up to eight different file types. ERDAS IMAGINE imports three types of ADRG data files:

  • .OVR (Overview)
  • .IMG (Image)
  • .Lxx (Legend or marginalia data)

Compressed ADRG (CADRG) is a different format, which may be imported or read directly.

ADRG .IMG and .OVR file formats are different from the ERDAS IMAGINE .img and .ovr file formats.

.OVR (overview)

The overview file contains a 16:1 reduced resolution image of the whole DR. There is an overview file for each DR.

Importing ADRG Subsets

Since DRs can be rather large, it may be beneficial to import a subset of the DR data for the application. Use ERDAS IMAGINE to define a subset of data from the preview image (see the "Subset Area with Overlapping ZDRs" figure below).

SHARED Tip You can import from only one ZDR at a time. If a subset covers multiple ZDRs, they must be imported separately and mosaicked using Mosaic option.

ADRG Overview File Displayed in a Viewer

adrgex

The white rectangle in the figure below represents the DR. The subset area in this illustration would have to be imported as three files: one for each zone in the DR.

Notice how the ZDRs overlap. Therefore, the .IMG files for Zones 2 and 4 would also be included in the subset area.

Subset Area with Overlapping ZDRs

adrg_format_subset_area_diagram

.IMG (scanned image data)

The .IMG files are the data files containing the actual scanned hard-copy graphics. Each .IMG file contains one ZDR plus padding pixels. The Import function converts the .IMG data files to ERDAS IMAGINE file format (.img). The image file can then be displayed in a Viewer.

.Lxx (legend data)

Legend files contain a variety of diagrams and accompanying information. This is information that typically appears in the margin or legend of the source graphic.

SHARED Tip This information can be imported into ERDAS IMAGINE and viewed. It can also be added to a map composition using ERDAS IMAGINE Map Composer.

Each legend file contains information based on one of these diagram types:

  • Index (IN)—shows the approximate geographical position of the graphic and its relationship to other graphics in the region.
  • Elevation/Depth Tint (EL)—depicts the colors or tints using a multicolored graphic that represent different elevations or depth bands on the printed map or chart.
  • Slope (SL)—represents the percent and degree of slope appearing in slope bands.
  • Boundary (BN)—depicts the geopolitical boundaries included on the map or chart.
  • Accuracy (HA, VA, AC)—depicts the horizontal and vertical accuracies of selected map or chart areas. AC represents a combined horizontal and vertical accuracy diagram.
  • Geographic Reference (GE)—depicts the positioning information as referenced to the World Geographic Reference System.
  • Grid Reference (GR)—depicts specific information needed for positional determination with reference to a particular grid system.
  • Glossary (GL)—gives brief lists of foreign geographical names appearing on the map or chart with their English-language equivalents.
  • Landmark Feature Symbols (LS)—depict navigationally-prominent entities.

ARC System Charts

ADRG data are based on one of these chart types from the ARC system:

ARC System Chart Types

ARC System Chart Type

Scale

GNC (Global Navigation Chart)

1:5,000,000

JNC-A (Jet Navigation Chart - Air)

1:3,000,000

JNC (Jet Navigation Chart)

1:2,000,000

ONC (Operational Navigation Chart)

1:1,000,000

TPC (Tactical Pilot Chart)

1:500,000

JOG-A (Joint Operations Graphic - Air)

1:250,000

JOG-G (Joint Operations Graphic - Ground)

1:250,000

JOG-C (Joint Operations Graphic - Combined)

1:250,000

JOG-R (Joint Operations Graphic - Radar)

1:250,000

ATC (Series 200 Air Target Chart)

1:200,000

TLM (Topographic Line Map)

1:50,000

Each ARC System chart type has certain legend files associated with the images. Legend files associated with each chart type are checked in the following table.

Legend Files for ARC System Chart Types

ARC System Chart

IN

EL

SL

BN

VA

HA

AC

GE

GR

GL

LS

GNC

JNC / JNC-A

ONC

TPC

JOG-A

JOG-G / JOG-C

JOG-R

ATC

TLM

ADRG File Naming Convention

The ADRG file naming convention is based on a series of codes: ssccddzz

  • ss = chart series code (see table of ARC System charts)
  • cc = country code
  • dd = DR number on the CD-ROM (01-99). DRs are numbered beginning with 01 for the northwesternmost DR and increasing sequentially west to east, then north to south.
  • zz = zone rectangle number (01-18)

For example, in the ADRG filename JNUR0101.IMG:

  • JN = Jet Navigation. This ADRG file is taken from a Jet Navigation chart.
  • UR = Europe. The data is coverage of a European continent.
  • 01 = This is the first DR on the CD-ROM, providing coverage of the northwestern edge of the image area.
  • 01 = This is the first zone rectangle of the DR.
  • .IMG = This file contains the actual scanned image data for a ZDR.

SHARED Tip You may change this name when the file is imported into ERDAS IMAGINE.

Legend File Names

Legend file names include a code to designate the type of diagram information contained in the file (see the previous legend file description). For example, the file JNUR01IN.L01 means:

  • JN = Jet Navigation. This ADRG file is taken from a Jet Navigation chart.
  • UR = Europe. The data is coverage of a European continent.
  • 01 = This is the first DR on the CD-ROM, providing coverage of the northwestern edge of the image area.
  • IN = This indicates that this file is an index diagram from the original hard-copy graphic.
  • .L01 = This legend file contains information for the source graphic 01. The source graphics in each DR are numbered beginning with 01 for the northwesternmost source graphic, increasing sequentially west to east, then north to south. Source directories and their files include this number code within their names.

For more detailed information on ADRG file naming conventions, see Military Specification MIL-A-89007.

ADRI Data

ADRI (ARC Digital Raster Imagery), like ADRG data, are also from NGA and are currently available only to Department of Defense contractors. Data are in 128 × 128 tiled, 8-bit format, stored on 8 mm tape in band sequential format.

ADRI consists of SPOT panchromatic satellite imagery transformed into the ARC system and accompanied by ASCII encoded support files.

Like ADRG, ADRI data are stored in the ARC system in DRs. Each DR consists of all or part of one or more images mosaicked to meet the ARC bounding rectangle, which encloses a 1 degree by 1 degree geographic area. See the following figure. Source images are orthorectified to mean sea level using NIMA Level I Digital Terrain Elevation Data (DTED) or equivalent data (Air Force Intelligence Support Agency, 1991).

See ADRG File Format for more information on the ARC system.

Seamless Nine Image DR

adri_format_9_image_layout_diagram

In ADRI data, each DR contains only one ZDR. Each ZDR is stored as a single raster image file, with no overlapping areas.

There are six different file types that make up ADRI format: two types of data files, three types of header files, and a color test patch file. ERDAS IMAGINE imports two types of ADRI data files:

  • .OVR (Overview)
  • .IMG (Image)

ADRI .IMG and .OVR file formats are different from ERDAS IMAGINE .img and .ovr file formats.

.OVR (overview)

Overview file (.OVR) contains a 16:1 reduced resolution image of the whole DR. There is an overview file for each DR on a tape. The .OVR images show the mosaicking from the source images and the dates when the source images were collected. See the figure below. This does not appear on the ZDR image.

ADRI Overview File Displayed in a Viewer

adriex

.IMG (scanned image data)

The .IMG files contain the actual mosaicked images. Each .IMG file contains one ZDR plus any padding pixels needed to fit the ARC boundaries. Padding pixels are black and have a zero data value. The ERDAS IMAGINE Import function converts .IMG data files to ERDAS IMAGINE file format (.img). The image file can then be displayed in a Viewer. Padding pixels are not imported, nor are they counted in image height or width.

ADRI File Naming Convention

ADRI file naming convention is based on a series of codes: ssccddzz

  • ss = image source code:
    • SP (SPOT panchromatic)
    • SX (SPOT multispectral) (not currently available)
    • TM (Landsat Thematic Mapper) (not currently available)
  • cc = country code
  • dd = DR number on the tape (01-99). DRs are numbered beginning with 01 for the northwesternmost DR and increasing sequentially west to east, then north to south.
  • zz = zone rectangle number (01-18)

For example, in the ADRI filename SPUR0101.IMG:

  • SP = SPOT 10 m panchromatic image
  • UR = Europe. The data is coverage of a European continent.
  • 01 = This is the first Distribution Rectangle on the CD-ROM, providing coverage of the northwestern edge of the image area
  • 01 = This is the first zone rectangle of the Distribution Rectangle.
  • .IMG = This file contains the actual scanned image data for a ZDR.

SHARED Tip You may change this name when the file is imported into ERDAS IMAGINE. If you do not specify a file name, ERDAS IMAGINE uses the ADRI file name for the image.