Source: Nebraska Department of Natural Resources
Processed by: Data Bank (JH)
Digital Orthophoto Quadrangle (DOQ)
A digital orthophoto quadrangle is a remotely sensed image data for a quadrangle in which
displacement of features caused by terrain relief and sensor orientation have
been mathematically removed. An orthophoto thus combines the image
characteristics of a photograph with the geometric qualities of a map.
A quadrangle is a 7.5 -minute x 7.5 -minute region that conforms to 7.5 minute
of latitude and 7.5 minute of longitude on the earth surface as designated by USGS
on its topographic maps. A quarter-quadrangle is a 3.75 x 3.75 minute of associated
earth's topography.
Availability of DOQs (1999 NAPP)
The Nebraska Department of Natural Resources, in cooperation with the U. S.
Geological Survey, developed DOQs based on 1999 NAPP imagery and second generation of 10-meter DEMs.
The 1999 DOQs are developed both in UTM and State Plane coordinate systems referenced to North American
Datum of 1983. The coordinate distances are published in meters for UTM and both meters and feet for the State Plane system.
- for 1999 DOQs
- for 1999 - State Plane DOQs
The 1999 DOQQs are also available upon request from the Nebraska Department of Natural Resources.
Availability of DOQs (1993 NAPP)
A grayscale DOQ requires about 46 MB of storage space per 3.75- minute
quarter quadrangle. It is a voluminous amount of data required to be
transmitted for each DOQ. The DOQs are therefore, available upon request
only from the Nebraska Department of Natural Resources. The proccessed
data (NAD 83, UTM projections) is shipped and copied onto a CD media or 8mm
data tapes. Also, each DOQ coverage comes with associated header data
embedded into it. The DOQs are disseminated in two forms.
- Pre-packaged CDs for predefined regions or block of quadrangles.
- Custom CDs for user defined group of quadrangles, processed in user format
(BIL, TIFF, GIF, etc)
for
processing costs
Sample and explanation of
(28" X 45")
- for 1993 DOQs
DOQ Dataset/Coverage
The Nebraska Department of Natural Resources, in cooperation with the U.S.
Geological Survey, produced DOQs for the entire State of Nebraska. These DOQs
are developed from 1993 NAPP flight coverage flown under the National Aerial
Photography Program, and meet the U. S. National Standards. The aerial
photographs are exposed using 10-inch wide film at 20,000 feet above land
surface with 6-inch focal length camera, resulting in a 1:40,000 scale image.
The digital (scanned) image is rectified to orthographic projections by
processing each pixel through photogrammetric equations derived from
photo-identifiable GPS control points, camera calibration from orientation
parameters, and the digital elevation model database.
The aerial photographs are digitized and processed to produce 3.75 x 3.75
minute DOQs with 1-meter ground resolution and mapped to 1:12,000 scale
accuracy specifications. The image transformations are cast on the Universal
Transverse Mercator (UTM) projections based on the North American Datum of
1983 (NAD 83). Also, each DOQ image has between 50 to 300 meters of overedge
to facilitate tonal matching for mosaicing of adjacent maps or images.
Rectification Process
Horizontal and
vertical controls were used to establish positions and elevations for
reference and correlation purposes and as input to the aerotriangulation
process. The GPS controls, collected the Nebraska Department of Natural
Resources, were used to provide photoidentifiable surveyed ground controls
for ground reference, and the final aerotriangulation solution for the
project.
Available USGS photo-identifiable ground control points were used to
test the results of the aerotriangulation adjustment. External orientation
parameters derived from the aerotriangulation solution were used to provide
the horizontal control for each photograph. Vertical controls for the
ortho-rectification process were obtained from existing 30m or 10m DEM's.
Each image was scanned from film-stable source at a resolution of
25-30 micrometers (resampled to 1-meter ground resolution) and orthorectified
using a softcopy digital orthophoto rectification process.
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