recrad_c |

Table of contents## Procedurerecrad_c ( Rectangular coordinates to RA and DEC ) void recrad_c ( ConstSpiceDouble rectan[3], SpiceDouble * range, SpiceDouble * ra, SpiceDouble * dec ) ## AbstractConvert rectangular coordinates to range, right ascension, and declination. ## Required_ReadingNone. ## KeywordsCONVERSION COORDINATES ## Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- rectan I Rectangular coordinates of a point. range O Distance of the point from the origin. ra O Right ascension in radians. dec O Declination in radians. ## Detailed_Inputrectan are the rectangular coordinates of a point. ## Detailed_Outputrange is the distance of the point `rectan' from the origin. The units associated with `range' are those associated with the input `rectan'. ra is the right ascension of `rectan'. This is 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. `ra' is output in radians. The range of `ra' is [0, 2*pi]. dec is the declination of `rectan'. This is the angle from the XY plane of the ray from the origin through the point. `dec' is output in radians. The range of `dec' is [-pi/2, pi/2]. ## ParametersNone. ## ExceptionsError free. 1) If the X and Y components of `rectan' are both zero, the right ascension is set to zero. 2) If `rectan' is the zero vector, right ascension and declination are both set to zero. ## FilesNone. ## ParticularsNone. ## ExamplesThe 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 mtrans [ 3 ][ 3 ]; SpiceDouble v1950 [ 3 ]; SpiceDouble v2000 [ 3 ]; /. Convert RA and DEC to a 3-vector expressed in the B1950 frame. ./ radrec_c ( 1.0, ra, dec, v1950 ); /. We use the CSPICE routine pxform_c to obtain the transformation matrix for converting vectors between the B1950 and J2000 reference frames. Since both frames are inertial, the input time value we supply to pxform_c is arbitrary. We choose zero seconds past the J2000 epoch as the input value. ./ pxform_c ( "B1950", "J2000", 0.0, mtrans ); /. Transform the vector to the J2000 frame. ./ mxv_c ( mtrans, v1950, v2000 ); /. Find the RA and DEC of the J2000-relative vector. ./ ## RestrictionsNone. ## Literature_ReferencesNone. ## Author_and_InstitutionN.J. Bachman (JPL) J. Diaz del Rio (ODC Space) E.D. Wright (JPL) ## Version-CSPICE Version 1.1.3, 04-JUL-2021 (JDR) Edited the header to comply with NAIF standard. -CSPICE Version 1.1.2, 30-JUL-2003 (NJB) Various header corrections were made. -CSPICE Version 1.1.0, 22-OCT-1998 (NJB) Made input vector const. -CSPICE Version 1.0.0, 08-FEB-1998 (EDW) ## Index_Entriesrectangular coordinates to ra and dec rectangular to right_ascension and declination |

Fri Dec 31 18:41:11 2021