A Data Foundation For The National Spatial Data Infrastructure (1995) / Chapter Skim
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2 NSDI FOUNDATION
2 NSDI FOUNDATION
Pages 15-23
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From page 15... ...
The data that make up this foundation will create a convenient and common reference for the compilation of other spatial data. DEFINITION OF A FOUNDATION A useful metaphor to understand the needs for a NSDI foundation can be taken from building construction.
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From page 16... ...
Based on its members' collective experience, the MSC has identified three types of data as the foundation geodetic control, digital terrain elevation, and digital orthorectified imagery. Geodetic control is required to systematically register all other information with a locational component.
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Because of the availability of GPS (particularly differential GPS technologies) and their decreasing costs, highly accurate locations of newly acquired spatial data are being tied to geodetic control at an accelerating rate.
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or large-scale photogrammetric surveys to lower-accuracy data created by digitizing contours from paper topographic maps or from small-scale, high-altitude photogrammetric surveys. Regardless of the specific data sources, digital terrain models need to be tied to a geodetic control network.
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From page 19... ...
Digital Orthorectified Imagery Digital orthorectified images provide a picture of the landscape from which features can be referenced to one another. They are digital raster unages produced by differential rectification of aerial photography to geodetic control and terrain elevation data; all
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Expensive photogrammetric equipment and highly skilled technicians were needed to create the rectified stereo Images that have been used for decades. These images have been the primary sources for updating the USGS 1:24,000 quad paper maps.
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The DOQ was used to construct the perspective shown on the front cover of this report.
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At the local level, this imagery may be at a much higher resolution than that of the DOQ program, reflecting specific local information needs. At the state level, the needs for the Imagery are similar to those for the DOQs; however, current state imagery programs have resolutions ranging from 0.5 to i.2 m pixels, and some states use color infrared instead of the black and white image sources used in the DOQ program.
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From page 23... ...
This draft implementation plan was reviewed at a forum by the National Research Council's Committee on Geodesy, which issued the report, Forum on NOAA's National Spatial Reference System (1994) , National Academy Press, Washington, DC, 66 pp.
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