pltexp_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

```   void pltexp_c ( ConstSpiceDouble   iverts,
SpiceDouble        delta,
SpiceDouble        overts )
```

#### Abstract

```
Expand a triangular plate by a specified amount. The expanded
plate is co-planar with, and has the same orientation as, the
original. The centroids of the two plates coincide.
```

```
DSK
```

```
MATH
GEOMETRY
TOPOGRAPHY

```

#### Brief_I/O

```
Variable  I/O  Description
--------  ---  --------------------------------------------------
iverts     I   Vertices of the plate to be expanded.
delta      I   Fraction by which the plate is to be expanded.
overts     O   Vertices of the expanded plate.
```

#### Detailed_Input

```
iverts     is an array containing three vertices of a triangular
plate. Each vertex is a three-dimensional vector. The
elements

iverts[i][j], j = 0 ... 2

are, respectively, the X, Y, and Z components of the
ith vertex.

delta      is a fraction by which the plate is to be scaled.
Scaling is done so that the scaled plate has the
following properties:

-  it is co-planar with the input plate

-  its centroid coincides with that of the input
plate

-  its sides remain parallel to the corresponding
sides of the input plate

-  the distance of each vertex from the centroid is
(1+delta) times the corresponding distance for
the input plate
```

#### Detailed_Output

```
overts     is an array containing three vertices of the triangular
plate resulting from scaling the input plate.

If `ctroid' is the centroid (the average of the vertices)
of the input plate, then the ith vertex of `overts'

overts[i][j], j = 0 ... 2

is equal to

ctroid[j] + (1+delta)*( iverts[i][j] - ctroid[j] ),

j = 0 ... 2

```

```
None.
```

```
Error free.
```

```
None.
```

#### Particulars

```
This routine supports "greedy" ray-plate intercept algorithms.
Such algorithms attempt to ensure that false negatives---in which
occur. In such an algorithm, the plate of interest is expanded
slightly before the intersection test is performed.
```

#### Examples

```
The numerical results shown for these examples 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) Expand an equilateral triangle that lies in the plane

{ (x,y,z) : z = 7 }

Use an expansion fraction of 1.0; this doubles the size of
the plate.

Example code begins here.

/.
Example program pltexp_ex1
./
#include <stdio.h>
#include <math.h>
#include "SpiceUsr.h"

int main()
{
/.
Local variables
./
SpiceDouble             delta;
SpiceDouble             iverts;
SpiceDouble             overts;
SpiceDouble             s;

s     = sqrt( 3.0 ) / 2.0;

vpack_c (   s,  -0.5,  7.0, iverts );
vpack_c ( 0.0,   1.0,  7.0, iverts );
vpack_c (  -s,  -0.5,  7.0, iverts );

delta = 1.0;

pltexp_c ( iverts, delta, overts );

printf ( "\n"
"Vertices of input plate: \n"
" I1 = %20.12f %20.12f %20.12f\n"
" I2 = %20.12f %20.12f %20.12f\n"
" I3 = %20.12f %20.12f %20.12f\n",
iverts, iverts, iverts,
iverts, iverts, iverts,
iverts, iverts, iverts  );

printf ( "\n"
"Vertices of output plate: \n"
" O1 = %20.12f %20.12f %20.12f\n"
" O2 = %20.12f %20.12f %20.12f\n"
" O3 = %20.12f %20.12f %20.12f\n\n",
overts, overts, overts,
overts, overts, overts,
overts, overts, overts  );

return ( 0 );
}

When this program was executed on a PC/Linux/gcc/64-bit
platform, the output was:

Vertices of input plate:
I1 =       0.866025403784      -0.500000000000       7.000000000000
I2 =       0.000000000000       1.000000000000       7.000000000000
I3 =      -0.866025403784      -0.500000000000       7.000000000000

Vertices of output plate:
O1 =       1.732050807569      -1.000000000000       7.000000000000
O2 =       0.000000000000       2.000000000000       7.000000000000
O3 =      -1.732050807569      -1.000000000000       7.000000000000

Note that the height of the plate is unchanged, but the vectors
from the centroid to the vertices have doubled in length.

```

```
None.
```

```
None.
```

#### Author_and_Institution

```
N.J. Bachman    (JPL)
```

#### Version

```
-CSPICE Version 1.0.0, 29-FEB-2016 (NJB)
```

#### Index_Entries

```
expand triangular plate
```
`Wed Apr  5 17:54:40 2017`