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halfpi_c
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Procedure
Abstract
Required_Reading
Keywords
Brief_I/O
Detailed_Input
Detailed_Output
Parameters
Exceptions
Files
Particulars
Examples
Restrictions
Literature_References
Author_and_Institution
Version
Index_Entries

Procedure

   SpiceDouble halfpi_c ( void ) 

Abstract

 
   Return half 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 half the value of pi. 
 

Detailed_Input

 
   None. 
 

Detailed_Output

 
   The function returns half the value of pi (the ratio of 
   a circle's circumference to its diameter), determined by 
   the ACOS function. That is, 
 
         halfpi_c = acos ( -1.0 ) * 0.50 
 

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 subroutine shown below illustrates the use of halfpi_c. 
 
            void bftran ( ra, dec, w, tipm )
               {
 
                /. 
                Compute the transformation from inertial to body 
                fixed coordinates, given the directions of the north 
                pole and prime meridian of the body. 
                ./

                SpiceDouble   ra;
                SpiceDouble   dec; 
                SpiceDouble   w;
                SpiceDouble   tipm [3][3];
 
 
                /.
                The transformation is defined by the compund 
                rotation 
           
                  [W] [pi/2 - Dec] [RA + pi/2] 
                     3            1           3 
                ./


                rotate_c (        ra + halfpi_c(), 3, tipm );
                rotmat_c ( tipm, halfpi_c() - dec, 1, tipm );
                rotmat_c ( tipm, w,                3, tipm );
 
               } 
 

Restrictions

 
   None. 
 

Literature_References

 
   None. 
 

Author_and_Institution

   W.L. Taber      (JPL) 
   I.M. Underwood  (JPL) 
   E.D. Wright     (JPL)
 

Version

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

Index_Entries

 
   half the value of pi 
 
Wed Apr  5 17:54:36 2017