Answer: The following items are required to produce a digital orthophoto:
- a minimum of three ground positions that can be identified on the photograph to be
rectified,
- camera calibration parameters, such as the calibrated focal length and the coordinates of
the camera fiducials,
- a digital elevation model (DEM), and
- a digital image produced by scanning an aerial photograph with a precise, high-resolution
scanner.
The digital image is rectified to generate an orthophoto by processing items 1 through 3 for each
image picture element (pixel) using rigorous photogrammetric equations on a high-speed
computer. The finished product is a spatially accurate image with planimetric features represented
in their true geographic positions.
A DOQ can be incorporated into any geographic information system (GIS), which can manipulate
raster images. It functions exceptionally well as a cartographic base for displaying, generating, and
modifying digital planimetric data. |
U.S. Department of the Interior |
U.S. Geological Survey