A digital orthophoto is blend of aerial photography and georeferenced maps.
The USGS DOQs are automated to strict standards, and give a very accurate picture
of any given area. They serve a variety of purposes, from interim maps to field
references for Earth science investigations and analyses. The digital orthophoto is useful
as a layer of a geographic information system (GIS) and as a tool for revision of digital
line graphs and topographic maps. Unlike a standard aerial photograph, relief displacement
in orthophotos has been removed so that ground features are displayed in their true ground
position. This allows for the direct measurement of distance, areas, angles, and
positions. Also, an orthophoto displays features that may be omitted or generalized on
maps.
The National Aerial Photography Program (NAPP) imagery and NAPP-like photography are the
primary sources of aerial photography used in the production of
1-meter digital orthophotos for the National Digital Orthophoto Program (NDOP). NAPP
photography is quarter-quadrangle centered (3.75-minutes of latitude by
3.75-minutes of longitude in geographic extent) and taken at an aircraft altitude of
approximately 20,000 feet above mean terrain. The scale of the NAPP photography is
approximately 1:40,000. Orthophoto quadrangles may also be produced through the mosaicking
of digital orthophoto quarter-quadrangles. Color infrared (CIR) photography may be used as
a source. However, the resulting DOQ may either be a single black-and-white composite of
all bands or a color DOQ with all three bands. Although NAPP is the primary image source,
this does not prevent the use of additional aerial photographs or digital images in the
future.
Digital Orthophoto (DOQ) Data Sources
The EROS Data Center of the USGS at http://edc.usgs.gov/products/aerial/doq.html is the main distributor of DOQ data. The DOQ's are listed in the photography section. These pages uses Java scripts, and some older versions of Netscape or Internet Explorer may not work with the scripts.
Tools for Using Digital Orthophotos
Information on the GeoTIFF format, as well as links to a free viewer, can be found at http://mcmcweb.er.usgs.gov/sdts/index.html .
Tools and instructions to read JPEG formats into ArcView currently exist at http://www.dnr.state.mn.us/mis/gis/tools/arcview
Information on using BIL format DOQQ's can be found at http://www.fws.gov/data/gisconv/doqbil.html .
For additional information regarding this Web page, contact Chris Lett, in the Division of Information Resources and Technology Management, at Chris_Lett@fws.gov
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Keywords=GIS, data, photographic, DOQ
Last Modified January 03, 2001 08:42 AM