2007 Digital Orthophotography
In 2007, the North Central Texas Council of Governments facilitated the cooperative purchase of 6-inch resolution digital aerial photography (orthos) for the following 16 counties in North Central Texas: Collin, Dallas, Denton , Ellis, Erath, Hood, Hunt, Johnson, Kaufman, Navarro, Palo Pinto, Parker, Rockwall, Somervell, Tarrant and Wise.
The contractor for this project was Bohannan Huston. The orthos were collected in February and March 2007 and are available for purchase via the DFWMaps Marketplace according to the following price schedule.
Georeferenced TIFF images are sold in 3,000' x 2,000' tiles, or 0.215 square miles. Sample images and a shapefile of the tile structure may be downloaded below:
6-Inch Resolution Color Ortho Sample [TIFF format with world file; 47 MB]
1-Foot Resolution Color Ortho Sample [TIFF format with world file; 13 MB]
2-Foot Resolution Color Ortho Sample [TIFF format with world file; 3.6 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 [ArcView Shapefile]
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.
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.
|Altitude of Capture||4,800' above mean terrain|
|Focal Length||120 mm (4.72")|
|Imagery Scale||1"= 1015’ (Photo scale 1: 12190 )|
|Capture Period||January-March 2007|
|Conditions||Leaf off, cloud free, 30 degree to 20 degree sun angle|
|Coordinate System||Texas State Plane, North Central Zone|
|Horizontal Datum||NAD 83|
|Units||US Survey Feet|