Digital Orthophoto Quadrangle (DOQ)
A Digital Orthophoto Quadrangle (DOQ) is a digital, uniform-scale image created from aerial photos. It is a photographic map in which ground features are displayed in their true ground position because relief displacements caused by the camera and terrain of an aerial photograph have been removed. It combines the image characteristics of a photograph with the geometric qualities of a map; thus, it is possible to get direct measurements of distances, areas, angles, and positions from a DOQ.
What is the difference between an aerial photograph and an orthophoto?
For more information about DOQs, please visit http://craterlake.wr.usgs.gov/doq_brief.html.
A standard DOQ is distributed in a quarter section of a standard 7.5-minute quadrangles. The one meter resolution of the DOQ results in a very large file size. Each quarter quadrangle DOQ is ~50MB; the complete mosaicked DOQ for the Lake Tahoe Basin is ~3GB.
DOQs are often compressed with JPEG compression, but for distribution here, all the DOQs for the Lake Tahoe Basin have been mosaicked together and compressed with MrSID compression from LizardTech. The compressed MrSID file has been reduced from ~3GB to ~144MB, which is still too large for convenient download over a modem. Viewers are available for free from LizardTech on their website.
U.S. Department of the Interior
|| U.S. Geological Survey
|| National Mapping Information
|| Western Regional Geography|
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Last Modified: Thursday, 13-Dec-2012 16:09:16 EST (tm)
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