The CADRG File Reader

This section describes the classes of the IlvMaps library that allow you to read files with the CADRG format.

The Compressed ARC Digitized Raster Graphics (CADRG) format is a map format for scanned maps published by the U.S. National Imagery and Mapping Agency (NIMA). This map format has been designed to meet the requirements of digital cartography. Its structure is particularly suited to load-on-demand and allows you to select the coverage that is best adapted to a given display scale.

A CADRG volume is generally stored in an rpf directory. This directory is organized into subdirectories, each corresponding to a coverage. A coverage directory contains a set of files, each corresponding to a frame. A coverage corresponds to a map at a given scale and is itself divided into rectangular frames that correspond to an area of the map at that scale. The rpf directory also contains a table of contents file, named a.toc, that lists all the elements in the volume. A CADRG volume includes other general information, such as overviews of the area represented in the coverage, and one or more legend files.

Generally, CADRG coverages are in the geographic projection, except for the poles for which the azimuthal equidistant projection is more appropriate.