cspice_pltar

 Abstract I/O Examples Particulars Required Reading Version Index_Entries

#### Abstract

```
CSPICE_PLTAR computes the total area of a collection of triangular plates.

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

```

#### I/O

```
Given:

vrtces   is an array containing the plate model's vertices.

Elements

vrtces[0,i-1]
vrtces[1,i-1]
vrtces[2,i-1]

are, respectively, the X, Y, and Z components of
the ith vertex, where `i' ranges from 1 to m, the number
of triangular plates comprising the plate set.

This routine doesn't associate units with the
vertices.

plates   is an array containing 3-tuples of integers
representing the model's plates. The elements of
`plates' are vertex indices. The vertex indices are
1-based: vertices have indices ranging from 1 to
n, the number of vertices comprising the plate set.

The elements

plates[0,i-1]
plates[1,i-1]
plates[2,i-1]

are, respectively, the indices of the vertices
comprising the ith plate.

Note that the order of the vertices of a plate is
significant: the vertices must be ordered in the
positive (counterclockwise) sense with respect to
the outward normal direction associated with the
plate. In other words, if v1, v2, v3 are the
vertices of a plate, then

( v2 - v1 )  x  ( v3 - v2 )

points in the outward normal direction. Here
"x" denotes the vector cross product operator.

the call:

double = CSPICE_PLTAR( vrtces, plates )

returns:

pltar   The function returns the total area of the input set of
plates. Each plate contributes the area of the triangle
defined by the plate's vertices.

If the components of the vertex array have length unit L, then
the output area has units

2
L

```

#### 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.

Compute the area of the pyramid defined by the four
triangular plates whose vertices are the 3-element
subsets of the set of vectors:

( 0, 0, 0 )
( 1, 0, 0 )
( 0, 1, 0 )
( 0, 0, 1 )

PRO PLTAR_T

;;
;; Let the notation
;;
;;    < A, B >
;;
;; denote the dot product of vectors A and B.
;;
;; The plates defined below lie in the following planes,
;; respectively:
;;
;;    Plate 1:    { P :  < P, (-1,  0,  0) > = 0 }
;;    Plate 2:    { P :  < P, ( 0, -1,  0) > = 0 }
;;    Plate 3:    { P :  < P, ( 0,  0, -1) > = 0 }
;;    Plate 4:    { P :  < P, ( 1,  1,  1) > = 1 }
;;
vrtces =[ [ 0.D, 0.0, 0.0 ], \$
[ 1.D, 0.0, 0.0 ], \$
[ 0.D, 1.0, 0.0 ], \$
[ 0.D, 0.0, 1.0 ]  ]

plates =[ [ 1L, 4, 3 ], \$
[ 1, 2, 4 ], \$
[ 1, 3, 2 ], \$
[ 2, 3, 4 ]  ]

area = cspice_pltar( vrtces, plates )

print, 'Expected area  (3 + sqrt(3))/2 = 0.23660254037844384d+01'
print, 'Computed volume =  ', area

END

IDL outputs:

Expected area  (3 + sqrt(3))/2 = 0.23660254037844384d+01
Computed volume =         2.3660254

```

#### Particulars

```
This routine computes the total area of a set of triangular
plates. The plates need not define a closed surface.

Examples of valid plate sets:

Tetrahedron
Box
Tiled ellipsoid
Tiled ellipsoid with one plate removed
Two disjoint boxes
Two boxes with intersection having positive volume
Single plate
Empty plate set

```

```
ICY.REQ
DSK.REQ

```

#### Version

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

```

#### Index_Entries

```
compute plate model area

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