Convert from range, right ascension, and declination to rectangular coordinates.
VARIABLE I/O DESCRIPTION -------- --- --------------------------------------------------- range I Distance of a point from the origin. ra I Right ascension of point in radians. dec I Declination of point in radians. rectan O Rectangular coordinates of the point.
range is the distance of the point from the origin. Output units are the same as the units associated with `range.' ra is the right ascension of the input point: the angular distance measured toward the east from the prime meridian to the meridian containing the input point. The direction of increasing right ascension is from the +X axis towards the +Y axis. The range (i.e., the set of allowed values) of `ra' is unrestricted. Units are radians. dec is the declination of the point. This is the angular distance from the XY plane to the point. The range of `dec' is unrestricted. Units are radians.
rectan is the array containing the rectangular coordinates of the point. The output units associated with `rectan' are those associated with the input `range.'
The following code fragment converts right ascension and declination from the B1950 reference frame to the J2000 frame. #include "SpiceUsr.h" SpiceDouble ra; SpiceDouble dec; SpiceDouble r; SpiceDouble rotab [ 3 ][ 3 ]; SpiceDouble oldvec [ 3 ]; SpiceDouble newvec [ 3 ]; radrec_c ( 1.0, ra, dec, oldvec ); pxform_c ( "B1950", "J2000", 0.0, rotab ); mxv_c ( rotab, oldvec, newvec ); recrad_c ( newvec, &r, &ra, &dec );
N.J. Bachman (JPL) H.A. Neilan (JPL) E.D. Wright (JPL)
"Celestial Mechanics, A Computational Guide for the Practitioner" by Laurence G. Taff
-CSPICE Version 1.0.2, 28-JUL-2003 (NJB) Various header corrections were made. -CSPICE Version 1.0.1, 13-APR-2000 (NJB) Made some minor updates and corrections in the code example. -CSPICE Version 1.0.0, 08-FEB-1998 (EDW)
range ra and dec to rectangular coordinates right_ascension and declination to rectangular