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vpack_c

 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

```   vpack_c ( Pack three scalar components into a vector )

void vpack_c ( SpiceDouble   x,
SpiceDouble   y,
SpiceDouble   z,
SpiceDouble   v[3] )

```

#### Abstract

```   Pack three scalar components into a vector.
```

```   None.
```

#### Keywords

```   VECTOR

```

#### Brief_I/O

```   VARIABLE  I/O  DESCRIPTION
--------  ---  --------------------------------------------------
x,
y,
z          I   Scalar components of a vector.
v          O   Equivalent vector.
```

#### Detailed_Input

```   x,
y,
z           are the scalar components of a 3-dimensional vector.
```

#### Detailed_Output

```   v           is the equivalent vector, such that

v[0] = x
v[1] = y
v[2] = z
```

#### Parameters

```   None.
```

#### Exceptions

```   Error free.
```

#### Files

```   None.
```

#### Particulars

```   Basically, this is just shorthand notation for the common
sequence

v[0] = x;
v[1] = y;
v[2] = z;

The routine is useful largely for two reasons. First, it
reduces the chance that the programmer will make a "cut and
paste" mistake, like

v[0] = x;
v[0] = y;
v[0] = z;

Second, it makes conversions between equivalent units simpler,
and clearer. For instance, the sequence

v[0] = x * rpd_c();
v[1] = y * rpd_c();
v[2] = z * rpd_c();

can be replaced by the (nearly) equivalent sequence

vpack_c ( x, y, z,    v );
vscl_c  ( rpd_c(), v, v );
```

#### Examples

```   The numerical results shown for this example may differ across
platforms. The results depend on the SPICE kernels used as input
(if any), the compiler and supporting libraries, and the machine
specific arithmetic implementation.

1) Compute an upward normal of an equilateral triangle lying
in the x-y plane and centered at the origin.

Example code begins here.

/.
Program vpack_ex1
./
#include <math.h>
#include <stdio.h>
#include "SpiceUsr.h"

int main( )
{

/.
Local variables
./
SpiceDouble          normal [3];
SpiceDouble          s;
SpiceDouble          v1     [3];
SpiceDouble          v2     [3];
SpiceDouble          v3     [3];

s = sqrt(3.0)/2;

/.
Define the three corners of the triangle.
./
vpack_c (   s, -0.5, 0.0, v1 );
vpack_c ( 0.0,  1.0, 0.0, v2 );
vpack_c (  -s, -0.5, 0.0, v3 );

/.
Compute an upward normal of the triangle.
./
pltnrm_c ( v1, v2, v3, normal );

printf( "NORMAL =  %16.13f %16.13f %16.13f\n",
normal[0], normal[1], normal[2] );

return ( 0 );
}

When this program was executed on a Mac/Intel/cc/64-bit
platform, the output was:

NORMAL =   0.0000000000000  0.0000000000000  2.5980762113533
```

#### Restrictions

```   None.
```

#### Literature_References

```   None.
```

#### Author_and_Institution

```   N.J. Bachman        (JPL)
J. Diaz del Rio     (ODC Space)
I.M. Underwood      (JPL)
```

#### Version

```   -CSPICE Version 1.0.1, 16-JUL-2020 (JDR)

```   pack three scalar components into a vector
`Fri Dec 31 18:41:15 2021`