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vupack_c

Table of contents
 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

```   vupack_c ( Unpack three scalar components from a vector )

void vupack_c ( ConstSpiceDouble     v[3],
SpiceDouble        * x,
SpiceDouble        * y,
SpiceDouble        * z     )

```

#### Abstract

```   Unpack three scalar components from a vector.
```

#### Required_Reading

```   None.
```

#### Keywords

```   VECTOR

```

#### Brief_I/O

```   VARIABLE  I/O  DESCRIPTION
--------  ---  --------------------------------------------------
v          I   Input 3-dimensional vector.
x,
y,
z          O   Scalar components of the vector.
```

#### Detailed_Input

```   v           is a double precision 3-dimensional vector.
```

#### Detailed_Output

```   x,
y,
z           are the double precision scalar components of the
vector `v'. The following equalities hold:

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

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

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

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

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

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

can be replaced by the (nearly) equivalent sequence

vscl_c   ( rpd_c(),  v,   v  );
vupack_c ( v,  &x,  &y,  &z  );
```

#### Examples

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

1) Suppose that you have an instrument kernel that provides,
within a single keyword, the three frequencies used by the
instrument, and that you want to use these frequencies
independently within your code.

The following code example demonstrates how to use vupack_c
to get these frequencies into independent scalar variables.

Use the kernel shown below, an IK defining the three
frequencies used by an instrument with NAIF ID -999001.

KPL/IK

File name: vupack_ex1.ti

The keyword below define the three frequencies used by a
hypothetical instrument (NAIF ID -999001). They correspond
to three filters: red, green and blue. Frequencies are
given in micrometers.

\begindata

INS-999001_FREQ_RGB   = (  0.65,  0.55, 0.475 )
INS-999001_FREQ_UNITS = ( 'MICROMETERS'       )

\begintext

End of IK

Example code begins here.

/.
Program vupack_ex1
./
#include <stdio.h>
#include "SpiceUsr.h"

int main( )
{

/.
Local parameters.
./
#define IKNAME       "vupack_ex1.ti"
#define KEYWRD       "INS-999001_FREQ_RGB"

/.
Local variables.
./
SpiceDouble          ddata  [3];
SpiceDouble          red;
SpiceDouble          green;
SpiceDouble          blue;

SpiceInt             n;

SpiceBoolean         found;

/.
Load the instrument kernel.
./
furnsh_c ( IKNAME );

/.
Get the frequency data from the kernel pool.
./
gdpool_c ( KEYWRD, 0, 3, &n, ddata, &found );

if ( found )
{
vupack_c ( ddata, &red, &green, &blue );
printf( "Blue  (nm):  %5.2f\n", blue  * 1000.0 );
printf( "Green (nm):  %5.2f\n", green * 1000.0 );
printf( "Red   (nm):  %5.2f\n", red   * 1000.0 );
}
else
{
printf( "No data found in the kernel pool for %s\n", KEYWRD );
}

return ( 0 );
}

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

Blue  (nm):  475.00
Green (nm):  550.00
Red   (nm):  650.00
```

#### 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, 03-SEP-2020 (JDR)

Edited the header to comply with NAIF standard. Added complete
code example.

-CSPICE Version 1.0.0, 07-NOV-2006 (NJB)

Corrected header errors that claimed this routine
performs the function of vpack_c.

-CSPICE Version 1.0.0, 28-JUN-1999 (IMU) (NJB)
```

#### Index_Entries

```   unpack three scalar components from a vector
```
`Fri Dec 31 18:41:15 2021`