Digital Orthophoto Quadrangles

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Frequently anticipated questions:


What does this data set describe?

Title: Digital Orthophoto Quadrangles
Abstract:

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 metadata provided in the digital
orthophoto contain a wide range of descriptive
information including format source information,
production instrumentation and dates, and data to assist
with displaying and georeferencing the image. The
standard distribution format of DOQs will be JPEG
compressed images on CD-ROM by counties or special
regions. The reconstituted image from the CD-ROM will
exhibit some radiometric differences when compared to its
uncompressed original but will retain the geometry of the
uncompressed DOQ. Uncompressed DOQs are distributed on
tape.
  1. How should this data set be cited?

    U.S. Geological Survey, Unknown, Digital Orthophoto Quadrangles: U.S. Geological Survey, Reston, VA.

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -124.7333
    East_Bounding_Coordinate: -067.9500
    North_Bounding_Coordinate: 49.3833
    South_Bounding_Coordinate: 24.5333

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date: 22-Feb-1994
    Ending_Date: present
    Currentness_Reference: ground condition

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: remote-sensing image

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      This is a raster data set. It contains the following raster data types:

      • Dimensions, type Pixel

    2. What coordinate system is used to represent geographic features?

      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:

      UTM_Zone_Number: 10-19

      Transverse_Mercator:

      Scale_Factor_at_Central_Meridian: .09996

      Longitude_of_Central_Meridian: -123 00 00

      Latitude_of_Projection_Origin: 0.0

      False_Easting: 500000.

      False_Northing: 0.0

      Planar coordinates are encoded using row and column
      Abscissae (x-coordinates) are specified to the nearest 1
      Ordinates (y-coordinates) are specified to the nearest 1
      Planar coordinates are specified in meters

      The horizontal datum used is North American Datum 1983.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.257.

  7. How does the data set describe geographic features?

    Entity_and_Attribute_Overview:

    For DOQ's from panchromatic source each pixel contains an
    8-bit gray-scale value between 0-255. A value of 0 represents
    the color black while a value of 255 represents the color white.
    All values between 0 and 255 are repesented as a shade of gray
    varying from black to white. For color-infrared and natural color
    DOQs' a digital number from 0 to 255 will also be
    asssigned to each pixel but that number will refer to a color
    look-up table which will contain the RGB red, blue and green
    (RGB) values, each from 0 to 255, for that digital number. Areas
    where the rectification process is incomplete due to incomplete data
    (i.e., lack of elevation data, gaps), are represented with the numeric
    value of 0.
    Entity_and_Attribute_Detail_Citation:

    U.S. Department of the Interior, U.S. Geological Survey,
    guide for digital orthophotos: Reston, VA.


    A hypertext version is available at:
    URL: <http://edc.usgs.gov/glis/hyper/guide/usgs_doq>


    U.S. Department of the Interior, U.S. Geological Survey, 1992,
    Standards for digital orthophotos: Reston, VA.


    Softcopies in ASCII, WordPerfect, and PostScript format are available at:
    URL: <ftp://mapping.usgs.gov/pub/ti/DOQ/>



Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

  2. Who also contributed to the data set?

  3. To whom should users address questions about the data?


Why was the data set created?


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.


How was the data set created?

  1. From what previous works were the data drawn?

    DEM1 (source 1 of 4)
    U.S. Geological Survey, Unknown, digital elevation model: U.S. Geological Survey, Reston, VA.

    Type_of_Source_Media: cartridge tape
    Source_Contribution:

    Elevation data in the form of an ortho-DEM regridded
    to user-specified intervals and bounds.

    PHOTO1 (source 2 of 4)
    U.S. Geological Survey, Unknown, photo ID number: U.S. Geological Survey, Reston, VA.

    Type_of_Source_Media: cartridge tape
    Source_Scale_Denominator: 40000
    Source_Contribution:

    Panchromatic black and white (or color infra-red)
    NAPP or NAPP-like photograph. NAPP photographs are
    centered on the DOQ coverage area.

    CONTROL_INPUT (source 3 of 4)
    U.S. Geological Survey, Unpublished material, project ground and photo control: U.S. Geological Survey, Reston, VA.

    Type_of_Source_Media: various media
    Source_Contribution:

    Horizontal and vertical control used
    to establish positions and elevations for reference and
    correlation purposes.

    CAMERA_INPUT (source 4 of 4)
    U.S. Geological Survey, Unpublished material, report of calibration: U.S. Geological Survey, Reston, VA.

    Type_of_Source_Media: disc, paper
    Source_Contribution: camera calibration parameters

  2. How were the data generated, processed, and modified?

    Date: Unknown (process 1 of 1)

    The production procedures, instrumentation, hardware and software
    used in the collection of standard USGS DOQ's vary depending on systems
    used at the contract, cooperator or USGS production sites. The majority of
    DOQ datasets are acquired through government contract. The process step
    describes, in general, the process used in the production of standard
    USGS DOQ data sets.


    The rectification process requires, as input, a user parameter file to control
    the rectification process, a digital elevation model (DEM1) gridded to user
    specified bounds, projection, zone, datum and X-Y units, a scanned digital
    image file (PHOTO1) covering the same area as the DEM, ground X-Y-Z
    point values (CONTROL_INPUT) and their conjugate photo coordinates in
    the camera coordinate system, and measurements of the fiducial marks
    (CAMERA_INPUT) in the digitized image.


    The camera calibration report (CAMERA_INPUT) provides the focal
    length of the camera and the distances in millimeters from the camera's
    optical center to the camera's 8 fiducial marks. These marks define the frame
    of reference for spatial measurements made from the photograph.
    Ground control points (CONTROL_INPUT) acquired from ground surveys
    or developed in aerotriangulation, are third order class 1 or better, and meet
    National Map Accuracy Standard (NMAS) for 1:12,000-scale.
    Ground control points are in the Universal Transverse Mercator
    or the State Plane Coordinate System on NAD83. Horizontal and vertical
    residuals of aerotriangulated tie-points are equal to or less than 2.5 meters.
    Standard aerotriangulation passpoint configuration consists of 9
    ground control points, one near each corner, one at the center near each
    side and 1 near the center of the photograph, are used. The conjugate
    positions of the ground control points on the photograph are measured
    and recorded in camera coordinates.


    The raster image file (PHOTO_1) is created by scanning an
    aerial photograph film diapositive with a precision image scanner. An
    aperture of approximately 25 to 32 microns is used, with an aperture
    no greater than 32 microns permitted. Using 1:40,000-scale photographs,
    a 25-micron scan aperture equates to a ground resolution of 1-meter.
    The scanner converts the photographic image densities to gray scale values
    ranging from 0 to 255 for black and white photographs. Scan files with
    ground resolution less than 1 meter or greater than 1 meter but less
    than 1.28 meters are resampled to 1 meter.


    The principal elevation data source (DEM1) are standard DEM datasets
    from the National Digital Cartographic Data Base (NDCDB). DEM's that
    meet USGS standards are also produced by contractors to fulfill DOQ
    production requirements and are subsequently archived in the NDCDB.
    All DEM data is equivalent to or better than USGS DEM standard level 1.
    The DEM used in the production of DOQ's generally has a 30-meter grid
    post spacing and possesses a vertical RMSE of 7-meters or less. A DEM
    covering the extent of the photograph is used for the rectification.
    The DEM is traversed from user-selected minimum to maximum X-Y values and
    the DEM X-Y-Z values are used to find pixel coordinates in the digitized
    photograph using transformations mentioned above. For each raster
    image cell subdivision, a brightness or gray-scale value is obtained using
    nearest neighbor, bilinear, or cubic convolution resampling of the
    scanned image. The pixel processing algorithm is indicated in the
    header file . An inverse transformation relates the image coordinates
    referenced to the fiducial coordinate space back to scanner
    coordinate space. For those areas for which a 7.5-minute DEM is
    unavailable and relief differences are less than 150 feet, a planar-DEM
    (slope-plane substitute grid) may be used.


    Rectification Process: The photo control points and focal length are
    iteratively fitted to their conjugate ground control points using a
    single photo space resection equation. From this mathematical
    fit is obtained a rotation matrix of constants about the three
    axes of the camera. This rotation matrix can then be used to
    find the photograph or camera coordinates of any other ground
    X-Y-Z point. Next a two dimensional fit is made between the
    measured fiducial marks on the digitized photograph and their
    conjugate camera coordinates. Transformation constants
    are developed from the fit and the camera or photo
    coordinates are used in reverse to find their conjugate pixel
    coordiates on the digitized photograph.


    Quality Control: All data is inspected according to a
    quality control plan. DOQ contractors must meet DOQ standards
    for attribute accuracy, logical consistency, data completeness and

  3. What similar or related data should the user be aware of?


How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?


    During photographic reproduction of the source photography,
    limited analog dodging is performed to improve image quality.
    Analog dodging consists of holding back light from certain
    areas of the sensitized photographic material to avoid
    overexposure. The diapositive is inspected to insure clarity
    and radiometric uniformity. Diapositive image brightness
    values are collected with a minimum of image quality manipulation.
    Image brightness values may deviate from brightness values of
    the original imagery due to image value interpolation during
    the scanning and rectification processes.
    Radiometry is verified by visual inspection of the digital
    orthophoto quadrangle with the original unrectified image to
    determine if the digital orthophoto has the same or better
    image quality as the original unrectified input image.
    Slight systematic radiometric differences can be detected
    between adjacent DOQ files due primarily to differences in
    source photography capture dates and sun angles of aerial
    photography along flight lines. These differences can be
    observed in an image's general lightness or darkness when
    compared to adjacent DOQ file coverages.

  2. How accurate are the geographic locations?


    The DOQ horizontal positional accuracy and the assurance of that
    accuracy depend, in part, on the accuracy of the data inputs to the
    rectification process. These inputs consist of the digital elevation
    model (DEM),aerotriangulation control and methods, the photo source
    camera calibration, scanner calibration, and aerial photographs that
    meet National Aerial Photography Program (NAPP) standards. The
    vertical accuracy of the verified USGS format DEM is equivalent to or
    better than a USGS level 1 or 2 DEM, with a root mean square error
    (RMSE) of no greater than 7.0 meters. Field control is acquired by
    third order class 1 or better survey methods sufficiently spaced to
    meet National Map Accuracy Staandards (NMAS) for 1:12,000-scale
    products. Aerial cameras have current certification from the USGS,
    National Mapping Division, Optical Science Laboratory. Test
    calibration scans are performed on all source photography scanners.


  3. How accurate are the heights or depths?

  4. Where are the gaps in the data? What is missing?


    All DOQ imagery is visually inspected for completeness to ensure that no
    gaps, or image misplacement exist in the 3.75' image area or in overedge
    coverage. DOQ images may be derived by mosaicking multiple images, in
    order to insure complete coverage. All DOQ's are cloud free within the
    3.75' image area. Some clouds may, very infrequently, be encountered only
    in the overedge coverage. Source photography is leaf-off in deciduous
    vegetation regions. Void areas having a radiometric value of zero and
    appearing black may exist. These are areas for which no photographic
    source is available or result from image transformation from other
    planimetric systems to the Universal Transverse Mercator (UTM). In the
    latter case, the void sliver areas are on the outside edges of the
    overedge area. The data set field content of each DOQ header record
    element is validated to assure completeness prior to archiving in the
    NDCDB.

  5. How consistent are the relationships among the observations, including topology?


    All DOQ header data and image file sizes are validated by the Tape
    Validation System (TVS) software prior to archiving in the National
    Digital Cartographic Data Base (NDCDB). This validation procedure assures
    correct physical format and field values for header record elements.
    Logical relationships between header record elements are tested.



How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints: None
Use_Constraints:

None. Acknowledgement of the U.S. Geological Survey would be
appreciated in products derived from these data.


  1. Who distributes the data set? (Distributor 1 of 1)

    Earth Science Information Center, U.S. Geological Survey

    Complete list of Earth Science Information Centers at:



    URL: <http://mapping.usgs.gov/esic/esic_index.html>



    Reston, VA 20192

    1-888-ASK-USGS (voice)

    Hours_of_Service: 0800-1600
    Contact_Instructions:

    In addition to the address above there are other ESIC offices
    throughout the country. A full list of these offices is at:


    URL: <http://mapping.usgs.gov/esic/esic_index.html>


  2. What's the catalog number I need to order this data set?

    Digital Orthophotoquad

  3. What legal disclaimers am I supposed to read?


    Although these data have been processed successfully on a computer
    system at the U.S. Geological Survey no warranty expressed or
    implied is made by the USGS regarding the utility of the data on any
    other system, nor shall the act of distribution constitute any such
    warranty. The USGS will warrant the delivery of this product in
    computer-readable format and will offer appropriate adjustment
    of credit when the product is determined unreadable by correctly
    adjusted computer input peripherals, or when the physical medium
    is delivered in damaged condition. Requests for adjustments of
    credit must be made within 90 days from the date of this shipment
    from the ordering site.

  4. How can I download or order the data?


Who wrote the metadata?

Dates:
Last modified: Jan-1995
Metadata author:
U.S. Geological Survey
508 National Center
Reston, VA 20192

703 648 4543 (voice)

Metadata standard:
Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)


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