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dskn02_c
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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

   void dskn02_c ( SpiceInt               handle,
                   ConstSpiceDLADescr   * dladsc,
                   SpiceInt               plid,
                   SpiceDouble            normal[3] ) 

Abstract

 
   Compute the unit normal vector for a specified plate from a type 
   2 DSK segment. 
 

Required_Reading

 
   DAS 
   DSK 
 

Keywords

 
   DAS 
   DSK 
   FILES 
 

Brief_I/O

 
   Variable  I/O  Description 
   --------  ---  -------------------------------------------------- 
   handle     I   DSK file handle. 
   dladsc     I   DLA descriptor. 
   plid       I   Plate ID. 
   normal     O   Plate's unit normal vector. 
 

Detailed_Input

 
   handle         is the handle of a DSK file containing a type 2 
                  segment from which data are to be fetched. 
 
   dladsc         is the DLA descriptor associated with the segment 
                  from which data are to be fetched. 
 
   plid           is the plate ID. Plate IDs range from 1 to NP  
                  (the number of plates in the segment identified
                  by `dladsc'). 
 

Detailed_Output

 
   normal         is the normal vector associated with the plate 
                  designated by `plid'. The direction of `normal' is 
                  determined by the order of the plate's vertices; 
                  the vertices are presumed to be ordered in the 
                  right-handed (counterclockwise) sense about the 
                  normal direction. If the plate's vertices are
                  v1, v2, v3, then `normal' points in the direction

                     (v2 - v1) x ( v3 - v2 )

                  where "x" represents the cross product operator.
                    
                  The vector `normal' is expressed in the body-fixed
                  reference frame of the segment designated by
                  `dladsc'. The center of this frame is the origin of
                  the cartesian coordinate system in which the vertices
                  are expressed. Note that the frame center need not
                  coincide with the central body of the segment. Units
                  are km.
 
                  The vector has magnitude 1.
 
                  If an error occurs on the call, `normal' is
                  undefined.
 

Parameters

  
   See the header file
 
       SpiceDLA.h
 

Exceptions

 
   1) If the input handle is invalid, the error will be diagnosed by 
      routines in the call tree of this routine.  
 
   2) If a file read error occurs, the error will be diagnosed by 
      routines in the call tree of this routine. 
 
   3) If the input DLA descriptor is invalid, the effect of this 
      routine is undefined. The error *may* be diagnosed by routines 
      in the call tree of this routine, but there are no guarantees. 
 
   4) If `plid' is less than 1 or greater than the number of plates 
      in the segment, the error SPICE(INDEXOUTOFRANGE) is signaled. 
 
   5) This routine does not check for linear independence of the  
      plate's edges. The plate model is assumed to be geometrically 
      valid. 
 

Files

 
   See input argument `handle'. 
 

Particulars

 
   None. 
 

Examples

  
   1) Look up all the vertices associated with each plate 
      of the model contained in a specified type 2 segment. For each 
      plate, display the plate's vertices and normal vector.
 
      For this example, we'll show the context of this look-up: 
      opening the DSK file for read access, traversing a trivial, 
      one-segment list to obtain the segment of interest. 
  
      Example code begins here. 
 
         #include <stdio.h>
         #include "SpiceUsr.h"
         #include "SpiceDLA.h"
         #include "dsk_proto.h"

         int main()
         {   
            /.
            Constants 
            ./
            #define PBUFSIZ         10000
            #define FILSIZ          256

            /.
            Local variables 
            ./
            SpiceBoolean            found;

            SpiceChar               dsk  [ FILSIZ ];

            SpiceDLADescr           dladsc;

            SpiceDouble             normal [3];
            SpiceDouble             verts  [3][3];

            SpiceInt                handle;
            SpiceInt                i;
            SpiceInt                j;
            SpiceInt                n;
            SpiceInt                np;
            SpiceInt                nread;
            SpiceInt                nv;
            SpiceInt                nvtx;
            SpiceInt                plates[PBUFSIZ][3];
            SpiceInt                plix;
            SpiceInt                remain;
            SpiceInt                start;

            /.
            Prompt for name of DSK and open file for reading.
            ./
            prompt_c ( "Enter DSK name > ", FILSIZ, dsk );

            dasopr_c ( dsk,    &handle );

            dlabfs_c ( handle, &dladsc, &found );

            if ( !found )
            { 
               setmsg_c ( "No segment found in file #." );
               errch_c  ( "#",  dsk                     );
               sigerr_c ( "SPICE(NOSEGMENT)"            );
            }

            /.
            Get segment vertex and plate counts.
            ./
            dskz02_c ( handle, &dladsc, &nv, &np );

            printf ( "\n" 
                     "Number of vertices:  %d\n"
                     "Number of plates:    %d\n",
                     (int)nv,
                     (int)np                           );

            /.
            Display the vertices of each plate.
            ./
            remain = np;
            start  = 1;

            while ( remain > 0 )
            { 
               /.
               `nread' is the number of plates we"ll read on this
               loop pass.
               ./
               nread  = mini_c ( 2, PBUFSIZ, remain );

               dskp02_c ( handle, &dladsc, start, nread, &n, plates );

               for ( i = 0; i < nread; i++ )
               {
                  plix = start + i;

                  /.
                  Read the vertices of the current plate.
                  ./
                  for ( j = 0;  j < 3;  j++ )
                  {         
                     dskv02_c ( handle, &dladsc, plates[i][j],  
                                1,      &nvtx,   
                                ( SpiceDouble(*)[3] )(verts[j])  );
                  }

                  /.
                  Display the vertices of the current plate:
                  ./
                  printf ( "\n" 
                           " Plate number: %d\n"
                           "    Vertex 1: ( %16.8e %16.8e %16.8e )\n"
                           "    Vertex 2: ( %16.8e %16.8e %16.8e )\n" 
                           "    Vertex 3: ( %16.8e %16.8e %16.8e )\n",
                           (int)plix,
                           verts[0][0],  verts[0][1],  verts[0][2], 
                           verts[1][0],  verts[1][1],  verts[1][2], 
                           verts[2][0],  verts[2][1],  verts[2][2]   );

                  /.
                  Display the normal vector of the current plate:
                  ./
                  dskn02_c ( handle, &dladsc, plix, normal );

                  printf( "    Normal:   ( %16.8e %16.8e %16.8e )\n",
                          normal[0], normal[1], normal[2]           );
               }

               start  = start  + nread;
               remain = remain - nread;
            }

            /.
            Close the kernel.  This isn't necessary in a stand-
            alone program, but it's good practice in subroutines
            because it frees program and system resources.
            ./
            dascls_c ( handle );

            return ( 0 );
         } 

 
   When this program was executed on a PC/Linux/gcc/32bit 
   platform, using a DSK file representing a regular icosahedron, 
   the output was: 
 

      Number of vertices:  12
      Number of plates:    20

       Plate number: 1
          Vertex 1: (   0.00000000e+00   0.00000000e+00   1.17557000e+00 )
          Vertex 2: (   1.05146000e+00   0.00000000e+00   5.25731000e-01 )
          Vertex 3: (   3.24920000e-01   1.00000000e+00   5.25731000e-01 )
          Normal:   (   4.91124160e-01   3.56821347e-01   7.94654382e-01 )

       Plate number: 2
          Vertex 1: (   0.00000000e+00   0.00000000e+00   1.17557000e+00 )
          Vertex 2: (   3.24920000e-01   1.00000000e+00   5.25731000e-01 )
          Vertex 3: (  -8.50651000e-01   6.18034000e-01   5.25731000e-01 )
          Normal:   (  -1.87592328e-01   5.77350079e-01   7.94654645e-01 )

          ...

       Plate number: 20
          Vertex 1: (   8.50651000e-01  -6.18034000e-01  -5.25731000e-01 )
          Vertex 2: (   0.00000000e+00   0.00000000e+00  -1.17557000e+00 )
          Vertex 3: (   8.50651000e-01   6.18034000e-01  -5.25731000e-01 )
          Normal:   (   6.07061680e-01   0.00000000e+00  -7.94654715e-01 )
  
 

Restrictions

 
   See Exceptions. 
 

Literature_References

 
   None. 
 

Author_and_Institution

 
   N.J. Bachman    (JPL) 
 

Version

 
   -CSPICE Version 1.0.1, 27-JAN-2016 (NJB)

      Edit to example program to use "%d" with explicit casts
      to int for printing SpiceInts with printf.
       
      Updated header Detailed_Output and Index_Entries
      sections.

   -CSPICE Version 1.0.0, 03-JUN-2010 (NJB)

Index_Entries

 
   compute normal vector for a type 2 dsk plate 
   compute normal vector from dsk type 2 plate id
 
Wed Apr  5 17:54:32 2017