Digital Orthophotography - Principles, Project design Issues,Utility, Accuracy, Economicsby John H. Michael, Senior Project Manager, InterMap Technologies, Ottawa, Canada.
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John Michael |
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Abstract : |
Digital orthopotography has gained widespread acceptance as the "land base" in many large and medium scale GIS applicatons. The paper begins with an outline of the applicability and utility of orthorectified imagery within a GIS.
Definitive standards and specifications for the production of digital orthophotography do not yet exist, and orthophoto accuracy is the subject of considerable debate. The accuracy issues surround the applicability of traditional survey and photogrammetric mapping processes and standards to digital orthophoto. In addition to adapting photogrammetric mapping standards to define orthophoto practices, specifications are required for scanning, digital elevation model (DEM) compilation and rectification processes.
This paper investigates a number of considerations implicit in developing specifications for digital orthophoto projects.Emphasis is given to those issues associated with the digital elevation model used in the differential rectification process and to the layout of the aerial photography. The implications of specifications governing scanning are followed by a discussion of image distortions and problems associated with map revision using image base maps.
Finally the paper investigates the economics of digital orthophoto programs and discusses the relationships that exist among resolution, accuracy and cost.
John Michael - Profile :
John Michael is a mapping specialist with twenty years of hands-on experience in all phases of photogrammetric mapping programs from design to data analysis. He holds a B.Sc. in geography with a specialization in surveys and mapping and an M.B.A with a concentration in international business.
John has lived and worked in Canada, Nigeria, Egypt, Tanzania, Nepal and Jordan. Each of these assignments involved the implementation of a major mapping program. He has also worked on short-term assignments in a number of other countries as a consultant to the World Bank, national and state governments, internatonal aid agencies and private sector corporations.His consulting assignments have included automaton design for producton systems, environmental GIS programs, land and real estate registration systems, and the development of mapping standards and specifications for GIS program implementation.
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