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pltnrm_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

```   pltnrm_c ( DSK, compute outward normal of plate )

void pltnrm_c ( ConstSpiceDouble    v1[3],
ConstSpiceDouble    v2[3],
ConstSpiceDouble    v3[3],
SpiceDouble         normal[3] )

```

#### Abstract

```   Compute an outward normal vector of a triangular plate.
The vector does not necessarily have unit length.
```

```   DSK
```

#### Keywords

```   DSK
FILES
TOPOGRAPHY

```

#### Brief_I/O

```   VARIABLE  I/O  DESCRIPTION
--------  ---  --------------------------------------------------
v1,
v2,
v3         I   Vertices of a plate.
normal     O   Plate's outward normal vector.
```

#### Detailed_Input

```   v1,
v2,
v3          are vertices of a triangular plate.
```

#### Detailed_Output

```   normal      is an outward normal vector of the plate defined by
the input vertices. The order of the vertices is
used to determine the choice of normal direction:
the normal vector is

( v2 - v1 ) x ( v3 - v2 )
```

#### Parameters

```   None.
```

#### Exceptions

```   1)  The input plate may be degenerate: it may be a line segment
or a point. These are not considered to be erroneous inputs.
```

#### Files

```   None.
```

#### Particulars

```   This routine saves computation time by not scaling the output
vector to unit length. The caller can scale the vector using
the routine vhat_c.
```

#### 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 pltnrm_ex1
./

#include <stdio.h>
#include <math.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;

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 );

pltnrm_c ( v1, v2, v3, normal );

printf ( "NORMAL = %18.14f %18.14f %18.14f\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 =   0.00000000000000   0.00000000000000   2.59807621135332
```

#### Restrictions

```   None.
```

#### Literature_References

```   None.
```

#### Author_and_Institution

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

#### Version

```   -CSPICE Version 1.0.1, 10-AUG-2021 (JDR)

Edited header to comply with NAIF standard.

Changed code example output format for the solution to fit
within the -Examples section without modifications.

-CSPICE Version 1.0.0, 26-JAN-2016 (NJB)
```

#### Index_Entries

```   compute normal vector of triangular plate from vertices
```
`Fri Dec 31 18:41:10 2021`