2013 Digital Aerial Photography

The North Central Texas Council of Governments has facilitated the cooperative purchase of 4-band, 6-inch resolution digital aerial photography (orthos) for over 5,700 square miles of the NCTCOG region, including Collin, Dallas, Denton, Tarrant and Rockwall counties and portions of Hunt, Kaufman, Ellis, Johnson, Hood,  Parker and Wise counties. The orthos were collected in January and February 2013 and are available for purchase via www.dfwmaps.com according to the following price schedule.

All images are georeferenced TIFF files and are sold as whole tiles only; price per square mile is provided only as a reference. Each TIFF ortho tile is 3,000' x 2,000', or 0.215 square miles. Sample images and a shapefile of the tile structure may be downloaded below; all orders for 2013 orthophotography products can be placed via www.dfwmaps.com. Before placing an order, read the frequently asked questions.

6-inch Resolution Color Ortho Sample [TIFF format with world file; 55 MB]

TIFF orthophotography grid [ArcView Shapefile]

Specifications

The specifications have been provided by the contractor for this project, Woolpert.

Color aerial photography was acquired using Z/I Digital Mapping Cameras (Z/I DMC I for non-restricted airspace and DMC II230 for restricted airspace) which has been proven accurate for photogrammetry mapping by the USGS digital sensor evaluation program at Stennis, Mississippi. The flight design achieved a nominal ground-pixel resolution sufficient for developing 6" pixel orthophotography without oversampling. It was also designed with sufficient forward overlap and strip side laps to ensure total project area coverage. The following flight specifications were used for aerials.

The coverage area for 2013 includes Dallas, Fort Worth, and surrounding urban and rural counties totaling 5,777 square miles. Four areas of true orthoimagery were produced over the central business districts of Dallas and Fort Worth, as well as the IH-635/I-75 intersection and the Dallas North Tollway corridor from I-635 to Keller Springs Parkway, totaling approximately 24 square miles.

The horizontal datum used for this project was the North American Datum 1983 (NAD83), Texas State Plane Coordinate System, North Central Zone, and expressed in U.S. Survey Feet. The vertical datum used for this survey was the North American Vertical Datum 1988 (NAVD88). Control was established using Dallas and Fort Worth Virtual Reference Stations (VRS) .

Aerotriangulation was performed using industry-accepted procedures on an approved softcopy workstation to support the horizontal accuracy requirements of the digital orthophotography. The RMS of known ground points meets or exceeds 1.0 ft. in x, y, or z.

The imagery was produced using best available DEM data, including ACS data provided by NCTCOG and LiDAR/DEM data from the Texas Natural Resource Information System (TNRIS). The orthoimagery was colorbalanced and to radiometric parameters established during the Frisco, Texas, 4 square-mile pilot phase of the project. The most nadir part of every image was used in the mosaicking. Mosaic seam lines are created to ensure that joins do not cut hard detail where avoidable. Mosaic lines do not cross through above-ground structures unless unavoidable. Seams through or along streets are placed to avoid obscuring or artificially creating centerlines, curbs, and sidewalks. Quality control steps were performed during production of the orthoimagery to ensure the orthoimagery is inspected for compliance with required aesthetic and spatial criteria.

Woolpert produced 4-band digital orthoimagery with a 0.5-foot pixel resolution for the defined 5,777 square mile project area. The images were interactively mosaicked to produce imagery with consistent tone, density, and color balance. The project-wide imagery was delivered in TIFF format with accompanying world files. Full tiles were used for the entire project area; Woolpert used NCTCOG’s provided 2,000’ X 3,000’ tile grid for the 2013 project.

The final orthoimagery meets The American Society of Photogrammetry and Remote Sensing (ASPRS) Class I standard for 1"=100' scale mapping (GSD =.50 ft., limiting RMS error = 1.0 ft.). NCTCOG's review team inspected the orthoimagery using Woolpert’s SmartView Connect web-based quality assurance system, which allows reviewers to immediately communicate issues found in the imagery through placement of attributed polygons. Any non-conforming orthoimagery was corrected and posted to the application for approval by the review team. Upon approval by NCTCOG, the final orthoimagery was delivered tiled to the NCTCOG grid (2,000' x 3,000' tiles), in 4-band (RGB+NIR) TIFF format and 3-band (RGB) MrSID compressed format (Generation 2 , 18:1 compression ratio) and 4-band (RGB+NIR) TIFF format and 4-band (RGB) MrSID compressed format (Generation 4 , 18:1 compression ratio).

Metadata for 2013 Orthophotography

For questions about the 2013 digital aerial photography project, contact Shelley Stenoien at 817-695-9156 or via email.