Coordinates and Satellite Orbits
Coordinates and Satellite Orbits
Coordinates and Satellite Orbits
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2013/3/6Topocentric <strong>Coordinates</strong>Jyh-Ching Juang, EE, NCKUThe topocentric local tangent coordinate system is typicallyeither east-north-up (ENU) system or north-east-down (NED)system.The origin is at the location of the observer (topocentric).The reference plane is a local-level frame with its (n 1 , n 2 ) axes ina plane tangent to the reference ellipsoid <strong>and</strong> the n 3 axisperpendicular to that ellipsoid.In the ENU system, the n 1 -axis points to the east (E), the n 2 -axisnorth (N), <strong>and</strong> the n 3 -axis up (U).zThe observation <strong>and</strong> tracking ofthe satellite from the groundNUtracking station is generallyEh Pmade in the topocentriccoordinate system.yx11Coordinate TransformsJyh-Ching Juang, EE, NCKUThe transformation from the ECEF frame to the navigation ENUframe is given by sincos0 n' ' ' 'C eR 3 ( /2) R 2 ( /2 ) R3( )cos sin sin sin cos' ' 'coscos sin cos sinThe transformation matrix from the ECI frame to the ENU frameis thusC R ( /2 ) R ( /2 ' ) R ( )ni3 2 3e3,i3r'n 2n 3n 1e 2i 1i 2e 1126
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