cspice_pltexp

 Abstract I/O Examples Particulars Required Reading Version Index_Entries

#### Abstract

```
CSPICE_PLTEXP expands 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.

For important details concerning this module's function, please refer to
the CSPICE routine pltexp_c.

```

#### I/O

```
Given:

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

delta    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

the call:

cspice_pltexp, iverts, delta, overts

returns:

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

is equal to

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

j = 0 ... 2

```

#### Examples

```
Any numerical results shown for this example may differ between
platforms as the results depend on the SPICE kernels used as input
and the machine specific arithmetic implementation.

PRO pltexp_t

s     = sqrt( 3.D ) / 2.D

iverts = [ [ s, -0.5D,  7.0], [ 0.0, 1.0, 7.0], [ -s, -0.5, 7.0] ]

delta = 1.D

cspice_pltexp, iverts, delta, overts

print,  'Vertices of input plate: '
print,  ' I1 = ', iverts(*,0)
print,  ' I2 = ', iverts(*,1)
print,  ' I3 = ', iverts(*,2)
print

print,  'Vertices of output plate: '
print,  ' O1 = ', overts(*,0)
print,  ' O2 = ', overts(*,1)
print,  ' O3 = ', overts(*,2)

END

IDL outputs:

Vertices of input plate:
I1 =       0.86602540     -0.50000000       7.0000000
I2 =        0.0000000       1.0000000       7.0000000
I3 =      -0.86602540     -0.50000000       7.0000000

Vertices of output plate:
O1 =        1.7320508      -1.0000000       7.0000000
O2 =        0.0000000       2.0000000       7.0000000
O3 =       -1.7320508      -1.0000000       7.0000000

```

#### Particulars

```
This routine supports "greedy" ray-plate intercept algorithms.
Such algorithms attempt to ensure that false negatives---in which
an intersection is not found due to round-off error---do not
occur. In such an algorithm, the plate of interest is expanded
slightly before the intersection test is performed.

```

```
ICY.REQ

```

#### Version

```
-Icy Version 1.0.0, 15-DEC-2016, ML (JPL), EDW (JPL)

```

#### Index_Entries

```
expand triangular plate

```
`Wed Apr  5 17:58:02 2017`