Digital Orthophoto Quadrangles for Portions of Wyoming

DOQ's serve a variety of purposes, from interim maps to
field references for earth science investigations and
analysis. The DOQ is useful as a layer of a geographic
information system and as a tool for revision of digital
line graphs and topographic maps.

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.