A Numerical Method for Computing Lower and Upper Bounds on the Values of Unreported Local Accuracies in NAD 83 (NSRS2007)
As part of its mission as the steward of the National Spatial Reference System, the National Geodetic Survey (NGS) occasionally has to update coordinates of passive control marks in the official geometric datum, North American Datum of 1983 (NAD 83). The most recent realization of NAD 83, called NAD 83 (NSRS2007), was NGS' first attempt to implement Federal Geographic Data Committee's standards of reporting “local and network accuracies” on a geospatial product. In that realization, only “directly connected” (e.g., “concurrently surveyed”) points had a local accuracy reported via NGS “datasheets.” All points had network accuracies reported. Although local accuracies can be computed for either “directly connected” or “indirectly connected” pairs of points, this may only be done if correlation information is available between the two points; but this information is not generally available for any given pair of points in the NAD 83 (NSRS2007) adjustment. This paper successfully defines a “bounding equation” which will allow users to know the lower and upper possible limits of any unreported local accuracy between a pair of points, based simply on knowledge of the two points' network accuracies.
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Document Type: Research Article
Publication date: June 1, 2011