The North Central Texas Council of Governments has facilitated the purchase of digital aerial photography (orthos) for the following eight counties in North Central Texas: Collin, Dallas, Denton, Ellis, Kaufman, Navarro, Rockwall and Tarrant. The orthos are six-inch resolution and were collected from January to March of 2005. NCTCOG's contractor for this project is Bohannan Huston.
Members of NCTCOG and private entities may purchase 2005 orthophotography products according to the following price scale.
6-inch Digital Orthophotography
(Collin, Dallas, Denton, Ellis, Kaufman, Navarro, Rockwall, and Tarrant counties) |
$10.00 per ortho tile
[$46.46 per square mile] |
| 1-foot Digital Orthophotography |
$5.00 per ortho tile
[$23.23 per square mile] |
| 2-foot Digital Orthophotography |
$3.00 per ortho tile
[$13.94 per square mile] |
| 4-foot Digital Orthophotography |
$2.00 per ortho tile
[$9.29 per square mile] |
| 8-foot Digital Orthophotography |
$1.00 per ortho tile
[$4.65 per square mile] |
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 2005 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; 50 MB]
1-Foot Resolution Color Ortho Sample [TIFF format with world file; 14 MB]
2-Foot Resolution Color Ortho Sample [TIFF format with world file; 3.7 MB]
4-Foot Resolution Color Ortho Sample [TIFF format with world file]
8-Foot Resolution Color Ortho Sample [TIFF format with world file]
TIFF orthophotography grid - Shapefile, DXF file
Metadata for 2005 orthophotography [PDF]
Specifications
Color aerial photography were acquired using a Z/I Digital Mapping Camera (Z/I DMC) 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:
| Altitude of Capture |
4,500' above mean terrain |
| Focal Length |
120 mm (4.72") |
| Imagery Scale |
1"=950' (Photo scale 1:11,400) |
| Capture Period |
January-March 2005 |
| Conditions |
Leaf off, cloud free, optimum sun angle |
| Forward Overlap |
60% |
| Sidelap |
25% |
| Coordinate System |
Texas State Plane, North Central Zone |
| Horizontal Datum |
NAD 83 |
| Units |
US Survey Feet |
| Format |
TIFF or MrSID (1 MrSID tile = 120 TIFF tiles) |
Several urbanized areas require spot shots, or photos taken from directly overhead, to minimize building tilt. Ground and airborne GPS control are acquired under the supervision of a registered surveyor at sufficient density and accuracy to support production of digital orthophotography to the specifications required. Control is collected in Texas State Plane, North Central Zone, NAD 83, NAVD 88 (HARN), U.S. Survey Feet.
Aerotriangulation is performed using industry-accepted procedures on an approved softcopy workstation or analytical stereoplotter to support the horizontal accuracy requirements of the digital orthophotography. RMS of known ground points does not exceed 1 foot in x, y, or z.
The most nadir part of every image is 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.
Note: Participants who received MrSID files may need to download an extension to view Generation 3 MrSID files in ArcView 3.x or AutoCAD. Click here to download the extension.
For questions about purchasing 2005 digital aerial photography, contact Shelley Broyles at 817-695-9156 or via email.
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