A Perfect Base for a GIS: The Digital Orthophotoby Judith A. Dall, Photo Science, Inc, Gaithersburg, United States,
Abstract: A digital orthophoto is a rectified image with no relief displacement or radial distortion inherent in an aerial photo. One advantage of a digital orthophotography is that it can be used as an accurate base for a GIS/LIS system in which map overlays containing an array of pertinent information can be accurately registered. Digital orthophotos are a valuable tool for mapping agencies, planners, engineers, utility companies and others who use a geographic information system (GIS). Digital Orthophotos will provide all the information of a photograph, but at the same time allow the registration of vector maps used in a GIS. The advantage of a Digital Orthophoto is that it can be used in many ways not possible with unrectified aerial photos. These uses include: direct measurements such as lengths and areas interactively on the computer screen, profiling of the ground surface quickly and accurately, image processing techniques can be employed to enhance or extract information, change detection, and efficient and accurate GIS updating. This presentation explains in detail what a digital orthophoto is and how it is created. In addition, many of the advantages and uses of digital orthos in a GIS will be outlined. Questions about file sizes, resolution, and scanners will be addressed. Finally a comparison between conventional orthophotos generated using an optical-mechanical instrument will be made with the new digital orthophoto.
Subject Headings: Geographic information systems | Information systems | Mapping | Information management | Photography | Systems management | Displacement (mechanics)
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