cspice_twovec

 Abstract I/O Examples Particulars Required Reading Version Index_Entries
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```

#### Abstract

```
CSPICE_TWOVEC calculates the transformation matrix to the
right-handed reference frame having an input vector as a
specified axis and a second input vector lying in a
define coordinate plane.

For important details concerning this module's function, please refer to
the CSPICE routine twovec_c.

```

#### I/O

```
Given:

axdef    a double precision axis 3-vector

indexa   the integer index signifying 'axdef' (1, 2 or 3)

plndef   a second double precision 3-vector in the
same plane as axdef

indexp   the index of the second principle axis,
orthogonal to 'axdef' (1, 2 or 3)

the call:

cspice_twovec, axdef, indexa, plndef, indexp, mout

returns

mout    a double precision 3x3-matrix containing a
rotation matrix from the frame of the original
vectors to the new frame

```

#### Examples

```
Any numerical results shown for this example may differ between
platforms as the results depend on the SPICE kernels used as input
and the machine specific arithmetic implementation.

;;
;; A trivial example. Define the reference vectors...
;;
;;  The i unit vector
;;
axdef  = [ 1.d, 0.d, 0.d]
indexa = 1

;;
;;  The -j unit vector. For this example, any vector
;;  in the x-y plane will suffice.
;;
plndef = [ 0.d, -1.d, 0.d]
indexp = 2

;;
;; Calculate the transformation matrix. The new frame
;; has axdef as axis indexa, with plndef in the same
;; plane, the direction axis indexp in that plane
;; and orthogonal to axdef. A third direction vector
;; completes the right handed frame.
;;
cspice_twovec, axdef, indexa, plndef, indexp, mout
print, mout

IDL outputs:

1.0000000       0.0000000       0.0000000
0.0000000      -1.0000000       0.0000000
0.0000000       0.0000000      -1.0000000

```

```
None.

```

```
ICY.REQ

```

#### Version

```
-Icy Version 1.0.1, 23-SEP-2008, EDW (JPL)

Eliminated error in English.

-Icy Version 1.0.0, 16-JUN-2003, EDW (JPL)

```

#### Index_Entries

```
define an orthonormal frame from two vectors

```
`Wed Apr  5 17:58:04 2017`