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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

   SpiceDouble pltar_c ( SpiceInt           nv,
                         ConstSpiceDouble   vrtces [][3],
                         SpiceInt           np,
                         ConstSpiceInt      plates [][3]  )

Abstract

 
   Compute the total area of a collection of triangular plates. 
 

Required_Reading

 
   None. 
 

Keywords

 
   DSK 
   GEOMETRY 
   MATH 
 

Brief_I/O

 
   Variable  I/O  Description 
   --------  ---  -------------------------------------------------- 
   nv         I   Number of vertices. 
   vrtces     I   Array of vertices. 
   np         I   Number of triangular plates. 
   plates     I   Array of plates. 
 
   The function returns the total area of the set of plates. 
 

Detailed_Input

 
   nv             is the number of vertices comprising the plate set. 
 
   vrtces         is an array containing the plate model's vertices. 
                  Elements 
 
                     vrtces[i-1][0]
                     vrtces[i-1][1]
                     vrtces[i-1][2]
 
                  are, respectively, the X, Y, and Z components of 
                  the ith vertex, where i ranges from 1 to `nv'.
 
                  This routine doesn't associate units with the 
                  vertices. 
 
 
   np             is the number of triangular plates comprising the 
                  plate set. 
 
   plates         is an array containing 3-tuples of integers
                  representing the set of plates. The elements of
                  `plates' are vertex indices. The vertex indices are
                  1-based: vertices have indices ranging from 1 to
                  `nv'. The elements
 
                     plates[i-1][0]
                     plates[i-1][1]
                     plates[i-1][2]
 
                  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. 
 
                   

Detailed_Output

 
   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 
                             

Parameters

 
   None. 
 

Exceptions

 
   1) If the number of plates is less than 0, the error 
      SPICE(BADPLATECOUNT) is signaled. 
 
   2) If the number of plates is positive and the number of vertices 
      is less than 3, the error SPICE(TOOFEWVERTICES) is signaled. 
 
   3) If any plate contains a vertex index outside of the range
 
         [1, nv]
 
      the error SPICE(INDEXOUTOFRANGE) will be signaled.

Files

 
   None. 
 

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 
 
 

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) 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.


      /.
      PROGRAM EX1
      ./

      /.
      Compute the area of a plate model representing the pyramid
      with one vertex at the origin and the other vertices
      coinciding with the standard basis vectors.
      ./

      #include <stdio.h>
      #include "SpiceUsr.h"

      int main()
      {   
         /.
         Local constants 
         ./ 
         #define NVERT           4
         #define NPLATE          4

         /.
         Local variables 
         ./
         SpiceDouble             area;

         /.
         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 }

         ./
         SpiceDouble             vrtces[NVERT ][3] =

                                 { { 0.0, 0.0, 0.0 }, 
                                   { 1.0, 0.0, 0.0 }, 
                                   { 0.0, 1.0, 0.0 },
                                   { 0.0, 0.0, 1.0 }  };

         SpiceInt                plates[NPLATE][3] = 

                                 { { 1, 4, 3 }, 
                                   { 1, 2, 4 }, 
                                   { 1, 3, 2 },
                                   { 2, 3, 4 }  };

         area = pltar_c( NVERT, vrtces, NPLATE, plates );

         printf ( "Expected area  =    (3 + sqrt(3)) / 2\n" 
                  "               =    0.23660254037844384e+01\n" );
         printf ( "Computed area  =   %24.17e\n", area            );

         return ( 0 );
      }


   When this program was executed on a PC/Linux/gcc/64-bit platform, 
   the output was: 
 
 
      Expected area   =    (3 + SQRT(3)) / 2 
                      =    0.23660254037844384E+01 
      Computed area   =    2.3660254037844384 
 
 

Restrictions

 
   None. 
 

Literature_References

 
   None. 
 

Author_and_Institution

 
   N.J. Bachman    (JPL) 
 

Version

 
   -CSPICE Version 1.0.0, 24-OCT-2016 (NJB)

Index_Entries

 
   compute plate model area 
 
Wed Apr  5 17:54:40 2017