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: http://www.stsci.edu/~sontag/spicedocs/cspice/dvhat_c.html
Дата изменения: Sat Dec 17 06:08:48 2005 Дата индексирования: Sun Apr 10 23:24:46 2016 Кодировка: Поисковые слова: moon |
Find the unit vector corresponding to a state vector and the derivative of the unit vector.
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VARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- s1 I State to be normalized. sout O Unit vector s1 / |s1|, and its time derivative.
s1 This is any double precision state. If the position component of the state is the zero vector, this routine will detect it and will not attempt to divide by zero.
sout sout is a state containing the unit vector pointing in the direction of position component of s1 and the derivative of the unit vector with respect to time. sout may overwrite s1.
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Let s1 be a state vector with position and velocity components p and v respectively. From these components one can compute the unit vector parallel to p, call it u and the derivative of u with respect to time, du. This pair (u,du) is the state returned by this routine in sout.
Suppose that STATE gives the apparent state of a body with respect to an observer. This routine can be used to compute the instantaneous angular rate of the object across the sky as seen from the observers vantage. dvhat_c ( state, ustate ); vel[0] = ustate[3]; vel[1] = ustate[4]; vel[2] = ustate[5]; angular_rate = vnorm_c ( vel );
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Error free. 1) If s1 represents the zero vector, then the position component of sout will also be the zero vector. The velocity component will be the velocity component of s1.
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W.L. Taber (JPL) E.D. Wright (JPL)
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-CSPICE Version 1.0.0, 7-JUL-1999
State of a unit vector parallel to a state vector