Procedure

   void rotvec_c ( ConstSpiceDouble  v1    [3],
                   SpiceDouble       angle, 
                   SpiceInt          iaxis, 
                   SpiceDouble       vout  [3] ) 

Abstract

 
   Transform a vector to a new coordinate system rotated by angle 
   radians about axis iaxis.  This transformation rotates v1 by 
   -angle radians about the specified axis.
 

Required_Reading

 
   None.
 

Keywords

 
   ROTATION,  VECTOR 
 

Brief_I/O

 
   VARIABLE  I/O  DESCRIPTION 
   --------  ---  -------------------------------------------------- 
   v1        I    Vector whose coordinate system is to be rotated. 
   angle     I    Angle of rotation in radians. 
   iaxis     I    Axis of rotation (X=1, Y=2, Z=3). 
   vout      O    Resulting vector [angle]      * v1 expressed in 
                                          iaxis 
                  the new coordinate system. vout can overwrite v1. 
 

Detailed_Input

 
   v1      This is a vector (typically representing a vector fixed 
           in inertial space) which is to be expressed in another 
           coordinate system.  The vector remains fixed but the 
           coordinate system changes. 
 
   angle   The angle given in radians, through which the rotation 
           is performed. 
 
   iaxis   The index of the axis of rotation.  The X, Y, and Z 
           axes have indices 1, 2 and 3 respectively. 
 

Detailed_Output

 
   vout    This is the vector expressed in the new coordinate system 
           specified by the angle of rotation and axis. If 
           [angle]       represents the rotation matrix described by 
                  iaxis 
           the angle and axis, (refer to the routine ROTATE) 
           then vout = [angle]      * v1 
                              iaxis 
 

Parameters

 
   None. 
 

Exceptions

 
 
   1) If the axis index is not in the range 1 to 3 it will be treated 
      the same as that integer 1, 2, or 3 that is congruent to it mod 
      3. 
 

Files

 
   None 
 

Particulars

 
   A rotation about the first, i.e. x-axis, is described by 
 
   |  1        0          0      | 
   |  0   cos(theta) sin(theta)  | 
   |  0  -sin(theta) cos(theta)  | 
 
   A rotation about the second, i.e. y-axis, is described by 
 
   |  cos(theta)  0  -sin(theta)  | 
   |      0       1        0      | 
   |  sin(theta)  1   cos(theta)  | 
 
   A rotation about the third, i.e. z-axis, is described by 
 
   |  cos(theta) sin(theta)   0   | 
   | -sin(theta) cos(theta)   0   | 
   |       0          0       1   | 
 
   rotvec_c decides which form is appropriate according to the value 
   of iaxis and applies the rotation to the input vector. 
 

Examples

 
   Suppose that 
   v1 = (1.414, 0, 0), angle = PI/4, iaxis = 3 
   then after calling rotvec_c according to 
 
          rotvec_c (v1, angle, iaxis, vout) 
 
   vout will be equal to (1, -1, 0). 
 

Restrictions

 
   None 
 

Literature_References

 
   None 
 

Author_and_Institution

 
   W.M. Owen       (JPL) 
   W.L. Taber      (JPL) 
 

Version

 
   -CSPICE Version 1.1.1, 04-OCT-1999 (NJB)
 
      Procedure line and abstract and were changed to dispel the
      impression that the input vector is rotated by +angle
      radians about the specified axis.
 
   -CSPICE Version 1.1.0, 22-OCT-1998 (NJB)

      Made input vector const.

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

Index_Entries

 
   rotate a vector 
 

Link to routine rotvec_c source file rotvec_c.c