Procedure

   void recrad_c ( ConstSpiceDouble    rectan[3],
                   SpiceDouble       * range,
                   SpiceDouble       * ra,
                   SpiceDouble       * dec      ) 

Abstract

 
   Convert rectangular coordinates to range, right ascension, and
   declination.

Required_Reading

 
   None. 
 

Keywords

 
   CONVERSION,  COORDINATES 
 

Brief_I/O

 
   VARIABLE  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_Input

 
   rectan     The rectangular coordinates of a point. 
 

Detailed_Output

 
   range      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].
 

Parameters

 
   None. 
 

Exceptions

 
   Error 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.
 

Files

 
   None. 
 

Particulars

   None.
 

Examples

 
   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      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.
      ./
      recrad_c ( v2000, &r, &ra, &dec ); 

 

Restrictions

 
   None. 
 

Literature_References

 
   None. 
 

Author_and_Institution

 
   N.J. Bachman    (JPL)
   H.A. Neilan     (JPL) 
   E.D. Wright     (JPL)
 

Version

 
   -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_Entries

 
   rectangular coordinates to ra and dec 
   rectangular to right_ascension and declination 
 

Link to routine recrad_c source file recrad_c.c