Geometric analysis of an observer on a spherical earth and an aircraft or satellite
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2013-09-30
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Alternative Title:Project Memorandum - September 2013
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Abstract:This memorandum contains a large amount of technical detail. However, in significant contrast, ; it addresses an easily-understood and fundamental need in surveillance and navigation systems ; analysis — quantifying the geometry of two locations relative to each other and to a spherical ; earth. Here, geometry simply means distances and angles. Sometimes, distances are the lengths ; of straight lines; in other cases they are the lengths of arcs on the earth’s surface. Similarly, angles may be measured between lines on a plane or between lines on a spherical surface. ; Because the earth has an established latitude/longitude coordinate system, the approach that first ; comes to mind is to address this situation as a three-dimensional problem and use vector analysis. ; However, the approach preferred here is that, to simplify and clarify the analysis process, the ; three-dimensional problem should be re-cast as two separate two-dimensional problems: ; Vertical Plane Formulation (Section 1.2 and Chapter 3)*— This analysis considers ; the vertical plane containing the two locations of interest and the center of the earth. ; The two locations are unconstrained vertically, although one altitude must be known. ; Plane trigonometry is the natural analysis tool for this problem. Latitudes and ; longitudes are not involved, which is its biggest limitation. ; Spherical Surface Formulation (Section 1.3 and Chapter 4)— This analysis— ; which is sometimes called great-circle navigation —only considers two locations on ; the surface of a spherical earth. Spherical trigonometry is a natural analysis tool in ; this setting, and latitudes and longitudes are inherent in this method. A significant ; limitation of this analysis is that altitudes cannot be accounted for.
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