CADRG (Compressed ARC Digitized Raster Graphics) Reader/Writer

FME Format Type Identifier




Typical File Extensions


CADRG is a general-purpose product, comprising computer-readable digital map and chart images. It supports various weapons, C3I theater battle management, mission planning, and digital moving map systems. CADRG data is derived directly from ADRG and other digital sources through downsampling, filtering, compression, and reformatting to the Raster Product Format (RPF) Standard.

CADRG files are usually physically formatted within a National Imagery Transmission Format (NITF) message. The CADRG Reader can read CADRG files with or without the NITF message wrapper. The CADRG Writer can create CADRG datasets with or without the NITF message wrapper. These options available in the Writer Feature Type Parameters.

The CADRG reader and writer implement the following standards:

  • MIL-C-89038
  • MIL-STD-2411
  • MIL-STD-2411-1
  • MIL-STD-2411-2

CADRG image data is of appropriate size and quality for use in military command and control systems, ground-based force to unit-level mission planning systems, and aircraft cockpit “moving map” displays. The post-reduction filtering scheme emphasizes legibility of text and contour lines to ensure that displayed and printed digital maps are readable and distinct. CADRG is intended to satisfy the needs of a broad range of users in its compression ratio, display and print quality and displayed screen size.

The CADRG datasets shall conform to MIL-STD-2411. It normally will be produced directly from source maps of all scales by processing and re-formatting into a CADRG frame file structure. Miscellaneous scale maps and charts or non-DMA maps may be the source for CADRG production. The processing includes spatial reduction (pixel downsampling) with filtering, vector quantization image compression, and color quantization.

To permit direct use by aircraft cockpit displays, CADRG data is arranged in frames and subframes with constant pixel sizes, and overlaps that are consistent with limited memory and processing capabilities of avionics computers.

CADRG Product and System Requirements


FME Platform

Operating System


FME Form

FME Flow

FME Flow Hosted

Windows 64-bit

















Reader Overview

FME considers a single CADRG TOC file to be a dataset.

The CADRG TOC file contains the location and name of the frame files. The frame files are raster files containing pixel data.

Writer Overview

FME considers a CADRG destination dataset to be a container folder name. Each feature type has a subfolder inside the container folder. Inside each subfolder, there is a table of contents file A.TOC and one or more subfolders containing some frame files. The frame files and their subfolders are named according to the specification MIL-STD-2411.

All raster features of the same CADRG feature type are grouped under one table of contents file. Each raster feature represents one boundary rectangle, but when the extents of the raster feature overlap two or more zones, the raster feature will be broken down into multiple boundary rectangles, each of which covers the raster subset in one zone. According to the specification, adjacent zones overlap each other, and the raster data in the intersection area will be repeated in the two boundary rectangles. Since each zone has a specific vertical/horizontal intervals and resolutions, the boundary rectangles may need to be resampled.

Each boundary rectangle will be broken down into one or more frame files. Each frame file has a size of 1536 x 1536. When the number of rows or columns in a frame is less than 4, the writer will not create the frame file, since the writer requires at least 4 rows and columns to do the spatial compression. The three palettes have 216, 32, and 16 entries, respectively when the raster does not have a Nodata value, or 217, 33, and 17 entries, respectively, when the raster has a Nodata value. Each palette entry is a four-byte value RGBM. The first byte R contains the red intensity level, the second byte G contains the green intensity level, the third byte B contains the blue intensity level and the fourth byte M contains a monochrome (grayscale) intensity level, which is an arithmetic combination of red, green and blue intensity levels. The equation used to calculate the monochrome intensity level is: 0.299 (Red) + 0.587 (Green) + 0.114 (Blue).

In the palettes, the last entries (the 217th, 33rd, and 17th entries, respectively) are reserved for the Nodata value, or the “transparent” pixels, for cases where the data is missing or not available at the given geographic location. The RGBM values in the CADRG palette for the Nodata entry are 0, 0, 0, 0.

FME Raster Features

FME raster features represent raster data and use several concepts that are unlike those used in the handling of vector data.

For comprehensive information about how FME processes raster data, see Rasters.

The CADRG reader produces rasters with a single UInt8 band that has multiple palettes.

The CADRG writer accepts only rasters with a Red8 band, a Green8 band, and a Blue8 band.