Type Digital Data
These data were produced to support the Connecticut statewide mapping program.
This orthoimagery data set includes 0.25 ft 8-bit 4-band (RGB-NIR) digital orthoimage tiles in GeoTIFF format covering the entire state of Connecticut which is approximately 5241 square miles. The source imagery was acquired between 03272023 and 04132023 using an UltraCam Eagle Mark 3 sensor. 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 23,381 individual 2500 ft x 2500 ft tiles. The imagery was aerotriangulated and orthorectified to meet ASPRS accuracy standards for 3 inch (7.5cm) horizontal accuracy class. 179 surveyed ground control check points were used assess the horizontal accuracy. Dewberry Engineers, Inc.
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be aware that temporal changes may have occurred since this dataset was collected and that some parts of these data may no longer represent actual surface conditions.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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Dewberry Engineers, Inc.
Ground condition
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be aware that temporal changes may have occurred since this dataset was collected and that some parts of these data may no longer represent actual surface conditions.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.
No restrictions apply to these data.
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.
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.
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.
The horizontal accuracy was tested with 179 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 orthoimagery exceeds the ASPRS accuracy standards for 3 inch (7.5cm) horizontal accuracy class.
Tested 0.235 feet RMSEx.
The horizontal accuracy was tested with 179 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 orthoimagery exceeds the ASPRS accuracy standards for 3 inch (7.5cm) horizontal accuracy class.
Tested 0.198 feet RMSEy.
The horizontal accuracy was tested with 179 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 orthoimagery exceeds the ASPRS accuracy standards for 3 inch (7.5cm) horizontal accuracy class.
Tested 0.307 feet RMSEr.
There is no vertical component for orthophotos.
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. Orthoimages 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 orthoimage frames were mosaicked together. Standard ortho frames and true ortho frames were combined in the mosaicking process to create the final orthomosaic tiles. The orthoimages meet ASPRS horizontal accuracy standards.
Dewberry Engineers, Inc. performed a geodetic control survey in support of the digital orthophoto production project. A total of 179 points were used for QC testing. Please see the survey report for more information.
ground condition
Aerial imagery was acquired using a UltraCam Eagle Mark 3 camera. 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. Standard aerial imagery at 60% forward overlap/30% sidelap was exposed at an average altitude of 6367 feet above mean terrain. True ortho imagery at 80% overlap was exposed at an average altitude of 6197 feet above mean terrain in select areas.
ground condition
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.
ground condition
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.
publication date
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.
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