/*

-Procedure pltexp_c ( Plate expander )

-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. 
 
-Disclaimer
 
   THIS SOFTWARE AND ANY RELATED MATERIALS WERE CREATED BY THE 
   CALIFORNIA INSTITUTE OF TECHNOLOGY (CALTECH) UNDER A U.S. 
   GOVERNMENT CONTRACT WITH THE NATIONAL AERONAUTICS AND SPACE 
   ADMINISTRATION (NASA). THE SOFTWARE IS TECHNOLOGY AND SOFTWARE 
   PUBLICLY AVAILABLE UNDER U.S. EXPORT LAWS AND IS PROVIDED "AS-IS" 
   TO THE RECIPIENT WITHOUT WARRANTY OF ANY KIND, INCLUDING ANY 
   WARRANTIES OF PERFORMANCE OR MERCHANTABILITY OR FITNESS FOR A 
   PARTICULAR USE OR PURPOSE (AS SET FORTH IN UNITED STATES UCC 
   SECTIONS 2312-2313) OR FOR ANY PURPOSE WHATSOEVER, FOR THE 
   SOFTWARE AND RELATED MATERIALS, HOWEVER USED. 
 
   IN NO EVENT SHALL CALTECH, ITS JET PROPULSION LABORATORY, OR NASA 
   BE LIABLE FOR ANY DAMAGES AND/OR COSTS, INCLUDING, BUT NOT 
   LIMITED TO, INCIDENTAL OR CONSEQUENTIAL DAMAGES OF ANY KIND, 
   INCLUDING ECONOMIC DAMAGE OR INJURY TO PROPERTY AND LOST PROFITS, 
   REGARDLESS OF WHETHER CALTECH, JPL, OR NASA BE ADVISED, HAVE 
   REASON TO KNOW, OR, IN FACT, SHALL KNOW OF THE POSSIBILITY. 
 
   RECIPIENT BEARS ALL RISK RELATING TO QUALITY AND PERFORMANCE OF 
   THE SOFTWARE AND ANY RELATED MATERIALS, AND AGREES TO INDEMNIFY 
   CALTECH AND NASA FOR ALL THIRD-PARTY CLAIMS RESULTING FROM THE 
   ACTIONS OF RECIPIENT IN THE USE OF THE SOFTWARE. 
 
-Required_Reading
 
   DSK 
 
-Keywords
 
   MATH  
   GEOMETRY 
   TOPOGRAPHY 
 
*/

   #include "SpiceUsr.h"
   #include "SpiceZfc.h"
   #undef pltexp_c

   void pltexp_c ( ConstSpiceDouble   iverts[3][3],
                   SpiceDouble        delta,
                   SpiceDouble        overts[3][3] ) 
/*

-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
 
 
-Parameters
 
   None. 
 
-Exceptions
 
   Error free. 
 
-Files
 
   None. 
 
-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. 
    
-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[3][3];
            SpiceDouble             overts[3][3];
            SpiceDouble             s;

            s     = sqrt( 3.0 ) / 2.0;

            vpack_c (   s,  -0.5,  7.0, iverts[0] );
            vpack_c ( 0.0,   1.0,  7.0, iverts[1] );
            vpack_c (  -s,  -0.5,  7.0, iverts[2] );

            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[0][0], iverts[0][1], iverts[0][2], 
                     iverts[1][0], iverts[1][1], iverts[1][2], 
                     iverts[2][0], iverts[2][1], iverts[2][2]  );

            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[0][0], overts[0][1], overts[0][2], 
                     overts[1][0], overts[1][1], overts[1][2], 
                     overts[2][0], overts[2][1], overts[2][2]  );

            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. 
 
 
-Restrictions
 
   None. 
 
-Literature_References
 
   None. 
 
-Author_and_Institution
 
   N.J. Bachman    (JPL) 
 
-Version
 
   -CSPICE Version 1.0.0, 29-FEB-2016 (NJB)

-Index_Entries
 
   expand triangular plate 
 
-&
*/

{ /* Begin pltexp_c */
 

   /*
   Participate in error tracing.
   */
   chkin_c ( "pltexp_c" );


   pltexp_ ( ( doublereal * ) iverts,
             ( doublereal * ) &delta,
             ( doublereal * ) overts  );


   chkout_c ( "pltexp_c" );

} /* End pltexp_c */
