Procedure

   twopi_c ( Twice the value of pi ) 

   SpiceDouble twopi_c ( void )

Abstract

   Return twice the value of pi (the ratio of the circumference of
   a circle to its diameter).

Required_Reading

   None.

Keywords

   CONSTANTS

Brief_I/O

   The function returns twice the value of pi.

Detailed_Input

   None.

Detailed_Output

   The function returns twice the value of pi (the ratio of
   a circle's circumference to its diameter), determined by
   the ACOS function. That is,

           twopi = acos ( -1. ) * 2.

Parameters

   None.

Exceptions

   Error free.

Files

   None.

Particulars

   The first time the function is referenced, the value is computed
   as shown above. The value is saved, and returned directly upon
   subsequent reference.

Examples

   The code fragment below illustrates the use of twopi_c.

        /.
               The longitude of the ascending node is the angle
               between the x-axis and the node vector, n.
                                                       -
        ./
               node = acos ( n[0] / vnorm_c( n ) );

               if ( node < 0.D0 )
                  {
                  node = node + twopi_c();
                  }

Restrictions

   None.

Literature_References

   None.

Author_and_Institution

   J. Diaz del Rio     (ODC Space)
   W.L. Taber          (JPL)
   I.M. Underwood      (JPL)
   E.D. Wright         (JPL)

Version

   -CSPICE Version 1.0.1, 02-JUN-2021 (JDR)

       Edited the header to comply with NAIF standard.

   -CSPICE Version 1.0.0, 08-FEB-1998 (EDW) (WLT) (IMU)

Index_Entries

   twice the value of pi