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USGS Connecticut Orthoimagery; Orthophoto GeoTIFF tiles

Frequently-asked questions:

What does this data set describe?

USGS Connecticut Orthoimagery; Orthophoto GeoTIFF tiles

       Product: This orthoimagery data set includes 0.5 ft 16-bit 4-band (RGB-IR) digital orthoimage tiles in GeoTIFF format.
       Geographic Extent: Eight counties in Connecticut, covering approximately 5241 total square miles. 
       Dataset Description: The USGS Connecticut Orthoimagery project called for the planning, acquisition, processing, and derivative products of imagery data to be collected at a ground sample distance (GSD) of 0.5 ft. Project specifications are based on the American Society of Photogrammetry and Remote Sensing (ASPRS) standards. The data were developed based on a horizontal projection/datum of NAD 1983 2011 StatePlane Connecticut FIPS 0600 Ft US, Foot US. Orthoimagery data were delivered in 23381 individual 2500 ft x 2500 ft tiles as 0.5 ft 16-bit 4-band (RGB-IR) orthophoto tiles in GeoTIFF format.
       Ground Conditions: Imagery was collected in spring 2019, while no snow was on the ground and rivers were at or below normal levels. In order to post process the imagery data to meet task order specifications and meet ASPRS horizontal accuracy guidelines, Quantum Spatial, Inc. utilized a total of 168 ground control points to assess the horizontal accuracy of the data.

  1. How should this data set be cited?

    Quantum Spatial, Inc., 20200211, USGS Connecticut Orthoimagery; Orthophoto GeoTIFF tiles.

  2. What geographic area does the data set cover?

    Bounding coordinates:
    West: -73.7388617737
    East: -71.7783557224
    North: 42.0597604961
    South: 40.9737553697

  3. What does it look like?

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

    Beginning date: 20190324
    Ending date: 20190425
    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 5000 x 5000, type pixel

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

      The grid coordinate system used is State Plane Coordinate System 1983

      State Plane Coordinate System 1983
      SPCS zone identifier: 0600
      Lambert conformal conic projection parameters:
      Standard parallel: 41.2
      Standard parallel: 41.8666666667
      Longitude of central meridian: -72
      Latitude of projection origin: 40.8333333333
      False easting: 999999
      False northing: 499999.999998

      Planar coordinates are encoded using row and column.
      Abscissae (x-coordinates) are specified to the nearest 0.5.
      Ordinates (y-coordinates) are specified to the nearest 0.5.
      Planar coordinates are specified in Foot US.

      The horizontal datum used is D NAD 1983 2011.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257222101.

  7. How does the data set describe geographic features?

    Entity and attribute overview:
    Three band orthoimagery is organized in three color bands or channels which represent the red, green, and blue (RGB) portions of the spectrum. Four band orthoimagery is organized in four color bands or channels which represent the red, green, blue (RGB), and near infrared (IR) portions of the spectrum. Each image pixel is assigned a triplet or quadruplet of numeric values, one for each color band. Numeric values range from 0 to 255.

    Entity and attribute detail citation:
    U.S. Department of the Interior, U.S. Geological Survey, 1996, Standards for Digital Orthophotos: Reston, VA.
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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?

    Quantum Spatial, Inc.

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

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Why was the data set created?

These data depict geographic features on the surface of the earth. The dataset was created to current imagery data for Connecticut.

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How was the data set created?

  1. Where did the data come from?

    CONTROL (source 1 of 4)

    Sewall, 20200211, GPS Photo Control Survey.

    Type of source media: online
    Source contribution:
    Quantum Spatial performed a geodetic control survey in support of the digital orthophoto production project. A total of 168 points were used for QC testing. Please see the survey report for more information.

    PHOTO (source 2 of 4)

    Quantum Spatial, Inc., 20200211, Georeferenced Single Frames.

    Type of source media: external hard drive
    Source contribution:
    Aerial imagery was acquired using a UltraCam Eagle camera with a flight design that included a total of 116 flight lines. Aerial imagery was supplemented with the simultaneous acquisition of airborne GPS/IMU data, which captured the ground coordinate for the nadir point of each photograph. Aerial imagery was exposed at an altitude of 8650 feet above mean terrain.

    AT (source 3 of 4)

    Quantum Spatial, Inc., 20200211, Aerotriangulation.

    Type of source media: online
    Source contribution:
    Softcopy aerotriangulation was performed utilizing the airborne GPS/IMU data, GPS ground control and image coordinate measurements allowing the direct computation of the exterior orientation parameters for each image of the project.

    DEM (source 4 of 4)

    Quantum Spatial, Inc., 20200211, DEM.

    Type of source media: online
    Source contribution:
    A compilation of topographic land form elevation datasets developed using in-house LiDAR data and data from the National Elevation Dataset for use in developing digital ortho imagery.

  2. What changes have been made?

    Date: 20200211 (change 1 of 1)
    Orthophoto Processing: Utilizing all four bands [blue (B), green (G), red (R), and infrared (IR)] digital orthorectification was performed using bilinear interpolation algorithms resulting in a spatial and radiometric transformation of the digital image from line/sample space into NAD 1983 2011 StatePlane Connecticut FIPS 0600 Ft US, Foot US. The interior and exterior orientation parameters from the aerotriangulation process were used to project each pixel into the ground coordinate system, while the ortho grade DEM was used to correct for relief displacement. Radiometric correction software and techniques were used to create orthophoto files that minimize the appearance of image seams and without loss of feature signature. Orthophotos are checked for geometric accuracy, image quality, and are tonally balanced to produce a uniform contrast and tone across the entire project. The individual overlapping orthophoto frames were mosaicked together. The ortho photos meet ASPRS horizontal accuracy standards.

    Data sources used in this process:
    • Georefs
    • AT
    • Control
    • DEM

    Data sources produced in this process:
    • Orthos

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

  1. How well have the observations been checked?

    Radiometry is verified by visual inspection of the digital orthophoto. Slight systematic radiometric differences may exist between adjacent orthoimage files; these are due primarily to differences in source image capture dates and sun angles along flight lines. These differences can be observed in an image's general lightness or darkness when it is compared to adjacent orthoimage file coverages. Tonal balancing may be performed over a group of images during the mosaicking process which may serve to lighten or darken adjacent images for better color tone matching.

  2. How accurate are the geographic locations?

    The project specifications require that only horizontal accuracy be computed for orthoimagery files. The required accuracy meets or exceeds ASPRS standards. The horizontal accuracy was tested with 20 checkpoints located throughout the project area. These checkpoints were not used in the calibration or post-processing of the imagery data. The checkpoints were distributed throughout the project area and were surveyed using GPS techniques. See survey report for additional survey methodologies. The x and y positions of where the checkpoints fell on the orthoimagery were collected. These values were then compared to the surveyed control point x and y values.

  3. How accurate are the heights or depths?

    There is no vertical component for orthophotos.

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

    Orthoimages are visually inspected for completeness to ensure that no gaps or image misplacements exist within and between adjacent images. These images are derived by mosaicking multiple images to ensure complete coverage. Source imagery is cloud free.

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

    All GeoTIFF tagged data and image file sizes are validated using commercial GIS software to ensure proper loading before being archived. This validation procedure ensures correct physical format and field values for tagged elements. Seamlines and tile edges are visually inspected. Seamline mismatches are corrected unless the overall displacement is less than one pixel.

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How can someone get a copy of the data set?

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

Access constraints: No restrictions apply to these data.
Use constraints:
None. However, users should be aware that temporal changes may have occurred since this dataset was collected and that some parts of these data may no longer represent actual surface conditions. Users should not use these data for critical applications without a full awareness of their limitations. Acknowledgement of the organization providing these data to the public would be appreciated for products derived from these data.

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  1. Who distributes the data set?

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

  3. What legal disclaimers am I supposed to read?

  4. How can I download or order the data?

  5. Is there some other way to get the data?

  6. What hardware or software do I need in order to use the data set?

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Who wrote the metadata?

Last modified: 20200211

Metadata author:
Quantum Spatial, Inc.
523 Wellington Way
Lexington, KY 40503

859-277-8700 (voice)
859-277-8901 (FAX)
Hours of Service: Monday through Friday 8:00 AM to 5:00 PM (Eastern Time)

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

Metadata extensions used:
  • None.

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