Table of contents
CSPICE_PLTAR computes the total area of a collection of triangular plates.
Given:
vrtces an array containing the plate model's vertices.
help, vrtces
DOUBLE = Array[3,NV]
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 an array containing 3-tuples of integers representing the
model's plates.
help, plates
LONG = Array[3,NP]
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:
pltar = cspice_pltar( vrtces, plates )
returns:
pltar the total area of the input set of plates.
help, pltar
DOUBLE = Scalar
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
None.
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.
1) 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 )
Example code begins here.
PRO pltar_ex1
;;
;; 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 area = ', area
END
When this program was executed on a Mac/Intel/IDL8.x/64-bit
platform, the output was:
Expected area (3 + sqrt(3))/2 = 0.23660254037844384d+01
Computed area = 2.3660254
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
1) If the number of plates is less than 0, the error
SPICE(BADPLATECOUNT) is signaled by a routine in the call tree
of this routine.
2) If the number of plates is positive and the number of vertices
is less than 3, the error SPICE(TOOFEWVERTICES) is signaled by
a routine in the call tree of this routine.
3) If any plate contains a vertex index outside of the range
[1, nv]
where `nv' is the number of vertices, the error
SPICE(INDEXOUTOFRANGE) is signaled by a routine in the call
tree of this routine.
4) If any of the input arguments, `vrtces' or `plates', is
undefined, an error is signaled by the IDL error handling
system.
5) If any of the input arguments, `vrtces' or `plates', is not of
the expected type, or it does not have the expected dimensions
and size, an error is signaled by the Icy interface.
None.
None.
DSK.REQ
ICY.REQ
None.
J. Diaz del Rio (ODC Space)
M. Liukis (JPL)
E.D. Wright (JPL)
-Icy Version 1.0.1, 01-JUN-2021 (JDR)
Added -Parameters, -Exceptions, -Files, -Restrictions,
-Literature_References and -Author_and_Institution sections.
Edited the header to comply with NAIF standard. Corrected typo in
code example output.
Removed reference to the routine's corresponding CSPICE header from
-Abstract section.
Added arguments' type and size information in the -I/O section.
-Icy Version 1.0.0, 15-DEC-2016 (ML) (EDW)
compute plate model area
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