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CRCOG Orthoimagery

Frequently-asked questions:

What does this data set describe?

CRCOG Orthoimagery

This data is a collection of orthorectified aerial imagery. The orthorectified imagery was delivered in uncompressed tiled 8-bit format (4band RGBCIR). Project wide and county mosaics (MrSID Gen3 and Gen4) were also delivered at 20:1 ratios. The data was produced at the request of the Capitol Region Council of Governments of Connecticut by The Sanborn Map Company of Colorado Springs. This orthorectified imagery has a pixel resolution of 0.25'. The data was flown from March12 to April 16 of 2016 using an UltraCam Eagle camera. This data is within the Connecticut State Plane Coordinate System, Datum of NAD83 (2011) and is in US Survey Feet.

  1. How should this data set be cited?

    Shawn Benham, The Sanborn Map Company, 20170117, CRCOG Orthoimagery.

    Other citation details:
    remote-sensing image

  2. What geographic area does the data set cover?

    Bounding coordinates:
    West: -73.753
    East: -71.774
    North: 42.061
    South: 40.973

  3. What does it look like?

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

    Beginning date: 20160312
    Ending date: 20160416
    Currentness reference:
    Regions defined by the Capitol Region Council of Governments of Connecticut.

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

    Geospatial data presentation form: Final

  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:
      • type Pixel

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

      The map projection used is Lambert Conformal Conic.

      Projection parameters:
      Standard parallel: 41.2
      Standard parallel: 41.8
      Longitude of central meridian: -72.75
      Latitude of projection origin: 40.8
      False easting: 999999.9
      False northing: 499999.9
      Lambert Conformal Conic
      Planar coordinates are encoded using coordinate pair.
      Abscissae (x-coordinates) are specified to the nearest 0.25 Feet.
      Ordinates (y-coordinates) are specified to the nearest 0.25 Feet.
      Planar coordinates are specified in survey feet.

      The horizontal datum used is D North American 1983 (2011).
      The ellipsoid used is GRS 1980.
      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:
    Color orthophotos are comprised of pixels. Each pixel is assigned a value of 0 to 255. That number will refer to a color look-up table which contains red, green and blue (RGB) values, each from 0 to 255, for that pixel within the image.

    Entity and attribute detail citation:
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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?

    Capitol Region Council of Governments of Connecticut

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

    Erik D. Snowden
    Capitol Region Council of Governments of Connecticut
    IT/GIS Coordinator
    241 Main St
    Hartford, CT 06106

    860-522-2217 x 217 (voice)
    860-724-1274 (FAX)
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Why was the data set created?

Rectified orthoimagery is for public use. An orthoimage is useful as a layer of any geographic information system (GIS). It can function as a cartographic base for displaying, generating, and modifying associated digital planimetric data. Other applications include environmental impact assessments, disaster management, emergency evacuation planning, flood analysis, soil erosion assessment, facility management, ground-water and watershed analysis, right of way and road alignment, transportation network inventory and analysis, preliminary design studies, vegetation classification detection of physical features or attributes not possible at ground level, and a myriad of additional applications.

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How was the data set created?

  1. Where did the data come from?

    IMG (source 1 of 1)

    The Sanborn Mapping Company, Inc., 2016, Aerial Photography.

    Type of source media: Aerial Images
    Source contribution:
    The aerial imagery was captured with an UltraCam Eagle digital camera. The Eagle is a full frame digital camera system.  The aerial images are used to AT the project and the production of orthophotos.

  2. What changes have been made?

    Date: 201604 (change 1 of 8)
    New digital, color aerial imagery of the site is acquired using Microsoft UltraCAM Eagle aerial camera systems. Airborne GPS/IMU data is recorded along with the imagery.

    Person responsible for change:
    Shawn Benham
    The Sanborn Map Company, Inc.
    Program Manager
    1935 Jamboree Dr #100
    Colorado Springs, CO 80920

    (719)502-1296 (voice)
    719-502-1296 (voice)
    Hours of Service: 8 - 5 Eastern Time

    Date: 201610 (change 2 of 8)
    The digital aerial imagery was transferred from the UCEcamera to a Mass Storage Unit (MSU) and shipped to Sanborn's main facility in Colorado Springs.  Once downloaded, data is processed via Microsoft Ultramap software from the raw camera format to a 4-band unsharpened color image and a pan image. An application is executed that outputs the mid-exposure pulse for each image. At this point a POS file is processed photo files as input to the Aerial Triangulation process. Raw camera data files are archived on LTO3 tapes. The imagery is processed using UltraMap processing software to create a 4-band multispectural (RGBN) format. The images are archived (on LTO3 tapes) and removed from system when orthophotography production has been completed.

    Date: 201609 (change 3 of 8)
    Softcopy (Digital) Aerotriangulation: This task involved the densification of ground control points, measurement of photo coordinates, computation and block adjustment to solve for exterior orientation parameters of individual photographs necessary for ortho-rectification. New ground control locations surveyed by the Sanborn map company; a combination of photo-identical points and targeted points were used.  The ground control points were measured in a fully digital environment using softcopy stereoplotters and tie point and passpoints automatically generated. Analytical aerotriangulation computations and adjustment were done using Inpho Match-AT software, which is capable of performing bundle block adjustments using a rigorous least squares analysis, and possesses error detection and removal facilities. Systematic error corrections for lens distortion, earth curvature, and atmospheric refraction.  State-of-the-art software with highly sophisticated error-detection routines was used to perform the computation and bundle block adjustment. Trained aerial triangulation specialist analyzed both numerical printouts and graphical error vector output display to detect gaps or holes in the block due to missing tie points, pass points or ground control.

    Date: 201609 (change 4 of 8)
    The digital elevation model (DEM) data was provided by Sanborn, for the purpose of rectification of the imagery. LiDAR was used to create the DEM. The DEM is updated where needed to support accurate rectification of the orthoimagery.

    Date: 201611 (change 5 of 8)
    Orthorectification: This task involved orthorectification of the raw digital raster images that were created from processing of Microsoft Ultracam Eagle digital camera data. A number of image processing techniques were used to maximize the quality of the deliverable images. Digital orthoimagery was created by draping the un-rectified raster images over their corresponding digital terrain models. All relief displacement was removed from the raw image files at ground level on a pixel-by-pixel basis using mathamatical pixel manipulation and seams, yielding a set of orthorectified digital photo images.   Mosaicking was performed to ensure a perfect edge match between all orthoimage tiles. Seam lines were generated automatically and manually manipulated where necessary to ensure that no image flaws result from seam lines passing through tall structures.  Seamline calculations bring in radiometric values of the pixels that are used first and then the terrain is brought into the equation.  The software uses the radiometric values to go around cars and buildings the best it can.  If the software detects a substantial change in the surface (like steep hills to cliffs), the software will try to compensate with another image, to avoid smearing  of the imagery.  If the seams would not compensate for the surface change, it would create a smear or the hillside would be more stretched than it should be.  There will be, on occasion, patches of seams hiding these terrain changes.   All orthoimagery  tiles were generated butt joints, no overlaps nor gaps. Radiometric adjustment was performed to balance and match color tones, brightness and contrast of the imagery over the whole project. Color orthoimagery were produced 8-bit per channel, resulting in 8-bit RGBN, .tif/.tfw format with a pixel size of 0.25ft. Ortho tiles were generated according to the pre-approved orthoimagery  tile layout.

    Date: 201611 (change 6 of 8)
    Quality Control All orthophoto tiles were thoroughly inspected according to Sanborn QA/QC quality control procedures. Comprehensive visual inspection included looking for mosaicking, image smearing and color balancing across the entire project. The process is overseen by a ASPRS Certified Photogrammetrist.  The CP Overseeing production at Sanborn is Doug Zehr.

    Date: 201612 (change 7 of 8)
    Dataset moved.

    Date: 201701 (change 8 of 8)
    Metadata updated/imported

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

  1. How well have the observations been checked?


  2. How accurate are the geographic locations?

    Horizontal accuracy is based on ground control and digital elevation model data provided by Sanborn Map Company that was used in the production of the digital orthoimagery.

  3. How accurate are the heights or depths?


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

    The ortho image tiles are checked for missing pixels, gaps, overlaps and other anomalies generally associated with digital orthophoto products. Any discrepancies in the ortho tiles are resolved through the use of proprietary and industry editing tools. Once the images are copied to the deliverable media they are further checked for naming, image completeness, and ability to be loaded in ArcMap.

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

    The digital imagery for each acquisition sortie is differentially rectified to produce orthophotography at a resolution of 3in.  Once the imagery has passed quality control review, final radiometric adjustments are performed to create a uniform overall appearance.  The process is overseen by a ASPRS Certified Photogrammetrist (CP). The CP overseeing production at Sanborn is Doug Zehr.

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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: None. This data is in the public domain.
Use constraints:
None.  Users can copy, modify, distribute and perform work, even for commercial purposes, without requesting permission.

Distributor 1 of 1

  1. Who distributes the data set?

    Erik D. Snowden
    Capitol Region Council of Governments of Connecticut
    IT/GIS Coordinator
    241 Main st
    Hartford, CT 06106

    860-522-2217 (voice)
    860-724-1274 (FAX)

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

    Downloadable Data

  3. What legal disclaimers am I supposed to read?


  4. How can I download or order the data?

    • Availability in digital form:

    • Data format:
      in format Digital Size: .135
      Media you can order:FTP or Digital disk(format FTP or Copy)

    • Cost to order the data: n/a

  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: 20170117

Metadata author:
Shawn Benham
The Sanborn Mapping Co., Inc.
Project Manager
1935 Jamboree Drive, Suite 100
Colorado Springs, CO 80920-5358

(719)502-1296 (voice)

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

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