The North Central Texas Council of Governments has facilitated the cooperative purchase of 6-inch resolution digital aerial photography (orthos) for the Metropolitan Planning Area (MPA), which includes Collin, Dallas, Denton, Tarrant and Rockwall counties as well as portions of Kaufman, Johnson, Ellis and Parker counties. The orthos were collected in February and March 2009 and are available for purchase via www.dfwmaps.com according to the following price schedule.
| 6-inch Digital Orthophotography |
$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] |
Specifications
The specifications have been provided by the contractor for this project, Bohannan Huston.
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 for aerials and contours:
| Altitude of Capture |
4,800' above mean terrain |
| Focal Length |
120 mm (4.72") |
| Imagery Scale |
1"= 1015’ (Photo scale 1: 12190 ) |
| Capture Period |
February-March 2009 |
| Conditions |
Leaf off, cloud free, 30 degree to 20 degree sun angle |
| Forward Overlap |
60% |
| Sidelap |
25% |
| Coordinate System |
Texas State Plane, North Central Zone |
| Horizontal Datum |
NAD 83 |
| Units |
US Survey Feet |
| Format |
Undetermined |
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.
For questions about the 2009 digital aerial photography project, contact Shelley Stenoien at 817-695-9156 or via email.
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