Index Page dskn02_c

A B C D E F G H I J K L M N O P Q R S T U V W X

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

#### Link to routine dskn02_c source file dskn02_c.c

    Wed Apr  5 17:54:32 2017