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A Digital Orthophoto (Quarter) Quadrangle, also known as DOQ, is a rectified digital image of an aerial photograph with distortion and displacements removed and corrected for aircraft pitch, yaw and altitude, camera tilt, and terrain relief, thus conforming to the properties of an orthographic projection. The finished product is a spatially accurate image with ground features represented in their true planimetric positions. A DOQ is, therefore, a computer-generated image of an aerial photograph that combines the image characteristics of a photograph with the geometric qualities of a map. Also, the digital image is a GIS product that can be overlaid and manipulated like any other coverage or layer, and offers significant flexibility.

The aerial photographs are digitized and processed to produce 3.75 x 3.75 minute DOQs with 1-meter ground resolution and mapped to 1:12,000 scale accuracy specifications. The image transformations are cast on the Universal Transverse Mercator (UTM) projections based on the North American Datum of 1983 (NAD 83). Also, each DOQ image also between 50 to 300 meters of overedge to facilitate tonal matching for mosaicing of adjacent maps or images. A grayscale DOQ requires about 46 MB of storage space per 3.75- minute or quarter quadrangle region.

A Compressed DOQ, also known as COQ, is a Digital Orthophoto Quarter Quadrangle image that has been compressed using JPEG format. Since JPEG is a "lossy" image compression format, a COQ will have slightly less color separation or clarity than that of a DOQ. However, its resolution (1-meter pixel size) remains the same.

A COQ requires about 2 MB to 4 MB of storage space per 3.75- minute or quarter quadrangle region.

More DOQQ Info:
  • A Primer on SDTS Data
  • A Primer on DOQQs

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