2009 Digital Orthophotography
In 2009, the North Central Texas Council of Governments 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 contractor for this project was Bohannan Huston.The orthos were collected in February and March 2009 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:
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. 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|
|Coordinate System||Texas State Plane, North Central Zone|
|Horizontal Datum||NAD 83|
|Units||US Survey Feet|