Orthophotos combine the image characteristics of a photograph with the geometric qualities of a map. The primary digital orthophotoquad (DOQ) is a 1-meter ground resolution, quarter-quadrangle (3.75-minutes of latitude by 3.75-minutes of longitude) image cast on the Universal Transverse Mercator Projection (UTM) on the North American Datum of 1983 (NAD83).The geographic extent of the DOQ is equivalent to a quarter-quad plus The overedge ranges a minimum of 50 meters to a maximum of 300 meters beyond the extremes of the primary and secondary corner points. The overedge is included to facilitate tonal matching for mosaicking and for the placement of the NAD83 and secondary datum corner ticks. The normal orientation of data is by lines (rows) and samples (columns). Each line contains a series of pixels ordered from west to east with the order of the lines from north to south. The standard, archived digital orthophoto is formatted as four ASCII header records, followed by a series of 8-bit binary image data records. The radiometric image brightness values are stored as 256 gray levels ranging from 0 to 255. The standard distribution format of DOQs will be BIL images on CD-ROM or compressed JPEG for download. Currently only images for the Jackson Hole area via the Spatial Data and Visualization Center clearinghouse. An on-line image browser is available (see the on-line linkage above) for viewing available images for the state and may include downloading capability as more images come on-line. The compressed JPEG format will exhibit some radiometric differences when compared to its uncompressed original but will retain the geometry of the uncompressed DOQ.
