Index of Functions: A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X
vdist_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

```   vdist_c ( Vector distance )

SpiceDouble vdist_c ( ConstSpiceDouble v1[3],
ConstSpiceDouble v2[3] )

```

#### Abstract

```   Return the distance between two three-dimensional vectors.
```

```   None.
```

#### Keywords

```   VECTOR

```

#### Brief_I/O

```   VARIABLE  I/O  DESCRIPTION
--------  ---  --------------------------------------------------

v1,
v2         I   Two 3-vectors.

The function returns the distance between v1 and v2.
```

#### Detailed_Input

```   v1,
v2          are two vectors in three-dimensional space, the
distance between which is desired.
```

#### Detailed_Output

```   The function returns the distance between v1 and v2. This is
defined as

||  v1 - v2  ||,

where || x || indicates the Euclidean norm of the vector x.
```

#### Parameters

```   None.
```

#### Exceptions

```   Error free.
```

#### Files

```   None.
```

#### Particulars

```   This function is simply shorthand for the code

vsub_c ( v1, v2, diff );

dist = vnorm_c ( diff );

Using this function saves you the annoyance of declaring local
storage for the difference vector `diff'.

The Euclidean norm of a three-dimensional vector (x, y, z) is
defined as

1/2
2        2        2
(   x    +   y    +   z    ).

This number is the distance of the point (x, y, z) from the
origin. If `a' and `b' are two vectors whose components are

( a[0], a[1], a[2] )    and    ( b[0], b[1], b[2] ),

then the distance between `a' and `b' is the norm of the difference
a - b, which has components

(  a[0] - b[0],  a[1] - b[1],  a[2] - b[2]  ).

A related routine is vdistg_c, which computes the distance between
two vectors of general dimension.
```

#### Examples

```   The numerical results shown for these examples 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) Define two three-dimensional vectors and calculate the distance
between them.

Example code begins here.

/.
Program vdist_ex1
./
#include <stdio.h>
#include "SpiceUsr.h"

int main( )
{
/.
Local variables.
./
SpiceDouble             dist;

/.
Define the vectors, and calculate the distance between the
coordinates.
./
SpiceDouble             v1  [ 3 ]  = { 1.0, 0.0, 0.0 };
SpiceDouble             v2  [ 3 ]  = { 0.0, 1.0, 0.0 };

dist = vdist_c ( v1, v2 );
printf( " Distance between v1 and v2: %12.6f\n", dist );

return ( 0 );
}

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

Distance between v1 and v2:     1.414214

2) Given the planetocentric coordinates of a point on the surface of
Mars, compute the distance between that point and Phobos.

Use the meta-kernel shown below to load the required SPICE
kernels.

KPL/MK

File: vdist_ex2.tm

This meta-kernel is intended to support operation of SPICE
example programs. The kernels shown here should not be
assumed to contain adequate or correct versions of data
required by SPICE-based user applications.

In order for an application to use this meta-kernel, the
kernels referenced here must be present in the user's
current working directory.

The names and contents of the kernels referenced
by this meta-kernel are as follows:

File name                        Contents
---------                        --------
de430.bsp                        Planetary ephemeris
mar097.bsp                       Mars satellite ephemeris
pck00010.tpc                     Planet orientation and
naif0011.tls                     Leapseconds

\begindata

'mar097.bsp',
'pck00010.tpc',
'naif0011.tls'  )

\begintext

End of meta-kernel

Example code begins here.

/.
Program vdist_ex2
./
#include <stdio.h>
#include "SpiceUsr.h"

int main( )
{
/.
Local variables
./
SpiceChar             * epoch;

SpiceDouble             dist;
SpiceDouble             et;
SpiceDouble             lat;
SpiceDouble             lon;
SpiceDouble             lt;
SpiceDouble             pos    [ 3 ];
SpiceDouble             rover  [ 3 ];

/.
./
furnsh_c( "vdist_ex2.tm" );

/.
Define the point on the surface of Mars by its planetocentric
coordinates, and the epoch.
./
epoch  = "2018-07-25 17:14";
lon    =    8.544377 * rpd_c( );
lat    =   42.880602 * rpd_c( );

/.
Convert that point coordinates to rectangular.
./
latrec_c ( radius, lon, lat, rover );

/.
Convert the UTC epoch to ephemeris time.
./
str2et_c ( epoch, &et );

/.
Compute the position of Phobos with respect to Mars in IAU_MARS
body-fixed reference frame.
./
spkpos_c ( "PHOBOS", et,  "IAU_MARS", "NONE", "MARS",
pos,    &lt                              );

/.
Compute the distance between Phobos and the point on the surface
of Mars.
./
dist = vdist_c ( rover, pos );
printf( " Epoch: %s\n", epoch );
printf( " Distance between location and Phobos (km): %12.6f\n",
dist );

return ( 0 );
}

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

Epoch: 2018-07-25 17:14
Distance between location and Phobos (km):  7174.781393
```

#### Restrictions

```   None.
```

#### Literature_References

```   None.
```

#### Author_and_Institution

```   N.J. Bachman        (JPL)
J. Diaz del Rio     (ODC Space)
E.D. Wright         (JPL)
```

#### Version

```   -CSPICE Version 1.2.1, 25-AUG-2021 (JDR)

Edited the header to comply with NAIF standard.

Added two complete examples to the -Examples section.

-CSPICE Version 1.2.0, 22-OCT-1998 (NJB)

Made input vectors const. Removed #include of SpiceZfc.h.

-CSPICE Version 1.1.0, 06-MAR-1998 (EDW)

Removed non printing character.

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

#### Index_Entries

```   distance between 3-dimensional vectors
```
`Fri Dec 31 18:41:14 2021`