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Index Page dskmi2_c

Table of contents

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

       dskmi2_c ( DSK, make spatial index for type 2 segment )

       void dskmi2_c  ( SpiceInt            nv,
                        ConstSpiceDouble    vrtces[][3],
                        SpiceInt            np,
                        ConstSpiceInt       plates[][3],
                        SpiceDouble         finscl,
                        SpiceInt            corscl,
                        SpiceInt            worksz,
                        SpiceInt            voxpsz,
                        SpiceInt            voxlsz,
                        SpiceBoolean        makvtl,
                        SpiceInt            spxisz,
                        SpiceInt            work   [][2],
                        SpiceDouble         spaixd [],
                        SpiceInt            spaixi []    )

#### Abstract

       Make spatial index for a DSK type 2 segment. The index is returned
       as a pair of arrays, one of type SpiceInt and one of type
       SpiceDouble. These arrays are suitable for use with the DSK type 2
       writer dskw02_c.

#### Required_Reading

       DAS
       DSK

#### Keywords

       DAS
       DSK
       FILES
       PLATE
       TOPOGRAPHY

#### Brief_I/O

       VARIABLE  I/O  DESCRIPTION
       --------  ---  --------------------------------------------------
       nv         I   Number of vertices.
       vrtces     I   Vertices.
       np         I   Number of plates.
       plates     I   Plates.
       finscl     I   Fine voxel scale.
       corscl     I   Coarse voxel scale.
       worksz     I   Workspace size.
       voxpsz     I   Voxel-plate pointer array size.
       voxlsz     I   Voxel-plate list array size.
       makvtl     I   Vertex-plate list flag.
       spxisz     I   Spatial index integer component size.
       work      I-O  Workspace.
       spaixd     O   Double precision component of spatial index.
       spaixi     O   Integer component of spatial index.

#### Detailed_Input

       nv          is the number of vertices belonging to the input
                   set of plates.

       vrtces      is an array of coordinates of the vertices. Vertex
                   indices, also called "vertex numbers," are 1-based in
                   all languages supported by SPICE, and range from 1 to
                   `nv'. The ith vertex occupies elements [i-1][0:2] of
                   this array.

       np          is the number of plates in the input plate set.

       plates      is an array representing the triangular plates of a
                   shape model. The elements of `plates' are vertex
                   indices; vertex indices, as well as plate indices, are
                   1-based in all languages supported by SPICE. The vertex
                   indices of the ith plate occupy elements [i-1][0:2] of
                   this array.

       finscl      is the fine voxel scale. This scale determines the
                   edge length of the cubical voxels comprising the fine
                   voxel grid: the edge length `voxsiz' is approximately

                       finscl * {average plate extent}

                   where the extents of a plate are the respective
                   differences between the maximum and minimum
                   coordinate values of the plate's vertices.

                   The relationship between `voxsiz' and the average plate
                   extent is approximate because the `voxsiz' is adjusted
                   so that each dimension of the fine voxel grid is an
                   integer multiple of the coarse voxel scale.

                   See the -Particulars section below for further
                   information on voxel scales.

       corscl      is the coarse voxel scale. This integer scale is the
                   ratio of the edge length of coarse voxels to that of
                   fine voxels. The coarse scale must be large enough so
                   that the total number of coarse voxels does not exceed
                   SPICE_DSK02_MAXCGR (see the -Parameters section below).

       worksz      is the second dimension of the workspace array `work'.
                   `worksz' must be at least as large as the greater of

                      - the number of fine voxel-plate associations

                        This number is equal to

                           np * {average number of fine voxels
                                 intersected by each plate}

                      - the number of vertex-plate associations, if
                        the vertex-plate mapping is constructed.

                        This number is equal to

                           nv + ( 3 * np )

       voxpsz      is the size of the fine voxel-plate pointer array.
                   This array maps fine voxels to lists of plates that
                   intersect those voxels. `voxpsz' must be at least as
                   large as

                            3
                      corscl  * {number of non-empty coarse voxels}

       voxlsz      is the size of the fine voxel-plate list array. This
                   array contains, for each non-empty fine voxel, the
                   count of plates that intersect that voxel and the
                   IDs of those plates. `voxlsz' must be at least as large
                   as

                           `np' * {average number of fine voxels
                                 intersected by each plate}

                       +   {number of non-empty fine voxels}

       makvtl      is a logical flag that, when set to SPICETRUE, indicates
                   that a  vertex-plate association list is to be
                   constructed.

                   The amount of workspace that is needed may depend on
                   whether a vertex-plate association list is
                   constructed. When this list is constructed, the size
                   of the integer component of the spatial index is
                   increased by the size of the list and the size of a
                   vertex-plate pointer array; the total of these sizes
                   is

                      ( 2 * nv ) + ( 3 * np )

       spxisz      is the declared size of the output array `spaixi'. This
                   size must be at least as large as the sum of

                      - the fixed-size part of the integer component of
                        the index, which includes the coarse voxel grid;
                        this value is

                           SPICE_DSK02_IXIFIX

                      - the size `voxpsz' of the voxel-plate pointer array

                      - the size `voxlsz' of the voxel-plate association
                        list

                   plus, if the vertex-plate association list is
                   constructed,

                      - the size `nv' of the vertex-plate pointer array

                      - the size of the vertex-plate association list;
                        this size is

                           nv + ( 3 * np )

       work        is the workspace array. The array should be declared
                   with dimensions

                      (2, worksz)

                   See the description of `worksz' above.

#### Detailed_Output

       work        is the workspace array, modified by the operations
                   performed by this routine.

       spaixd,
       spaixi      are, respectively, the double precision and integer
                   components of the spatial index of the segment.

                   `spaixd' must be declared with size at least
                   SPICE_DSK02_IXDFIX.

                   `spaixi' must be declared with size at least `spxisz'.

#### Parameters

       See the header file

          SpiceDSK.h

       for declarations of DSK data type 2 (plate model) parameters.

       See the header file

          SpiceDLA.h

       for declarations of DLA descriptor sizes and documentation of the
       contents of DLA descriptors.

       See the header file

          SpiceDSK.h

       for declarations of DSK descriptor sizes and documentation of the
       contents of DSK descriptors.

#### Exceptions

       1)  If the fine voxel scale is non-positive, the error
           SPICE(BADFINEVOXELSCALE) is signaled by a routine in the call tree of
           this routine.

       2)  If the coarse voxel scale is less than 1, the error
           SPICE(BADCOARSEVOXSCALE) is signaled by a routine in the call tree of
           this routine.

       3)  If `nv' is less than 3 or greater than SPICE_DSK02_MAXVRT, the error
           SPICE(BADVERTEXCOUNT) is signaled by a routine in the call tree of
           this routine.

       4)  If `np' is less than 1 or greater than SPICE_DSK02_MAXPLT, the error
           SPICE(BADPLATECOUNT) is signaled by a routine in the call tree of
           this routine.

       5)  If the workspace size `worksz' is less than np+1, the error
           SPICE(WORKSPACETOOSMALL) is signaled by a routine in the call tree of
           this routine. This is merely a sanity check; normally the workspace
           will need to be substantially larger than this reference value. See
           the description of `worksz' in the header section -Detailed_Input
           above.

       6)  If the voxel-plate pointer array size `voxpsz' is less than 1, the
           error SPICE(PTRARRAYTOOSMALL) is signaled by a routine in the call
           tree of this routine. This is merely a sanity check; normally this
           pointer array will need to be substantially larger than this
           reference value. See the description of `voxpsz' in the header
           section -Detailed_Input above.

       7)  If the voxel-plate list array size `voxlsz' is less than np+1, the
           error SPICE(PLATELISTTOOSMALL) is signaled by a routine in the call
           tree of this routine. This is merely a sanity check; normally this
           array will need to be substantially larger than this reference value.
           See the description of `voxlsz' in the header section -Detailed_Input
           above.

       8)  If the size `spxisz' of the integer array `spaixi' is too small
           to contain its constituent structures, where the sizes
           of these structures are derived from the inputs

               `nv', `np', `voxpsz', `voxlsz'

           the error SPICE(INTINDEXTOOSMALL) is signaled by a routine in the
           call tree of this routine.

       9)  If there is insufficient room to create any of the data
           structures contained in the spatial index, an error is
           signaled by a routine in the call tree of this routine.

#### Files

       None.

#### Particulars

       Users planning to create DSK files should consider whether the
       SPICE DSK creation utility MKDSK may be suitable for their needs.

       This routine supports use of the DSK type 2 segment writer dskw02_c
       by creating the "spatial index" arrays required as inputs to that
       routine.

       A spatial index is a group of data structures that facilitates
       rapid high-level computations involving sets of plates. The data
       structures created by this routine are aggregated into arrays
       of type SpiceInt and type SpiceDouble.

       Voxel grids
       ===========

       A key geometric computation---probably the most important, as it
       serves as a foundation for other high-level computations---is
       finding the intersection of a ray with the plate set. DSK type 2
       segments use data structures called "voxel grids" as part of
       their indexing mechanism. There is a "coarse grid": a box that
       completely encloses a DSK type 2 segment's plate set, and which
       is composed of identically-sized cubes called "coarse voxels."
       Each coarse voxel in composed of smaller cubes called "fine
       voxels." When the term "voxel" is used without qualification, it
       refers to fine voxels.

       Type 2 DSK segments contain data structures that associate plates
       with the fine voxels intersected by those plates. These
       structures enable the type 2 DSK software to rapidly find plates
       in a given region of space.

       Voxel scales
       ============

       There are two voxel scales:

       -  The coarse voxel scale is the integer ratio of the
          edge length of a coarse voxel to the edge length of
          a fine voxel

       -  The fine voxel scale is the double precision ratio
          of the edge length of a fine voxel to the average
          extent of the plates in the input plate set. "Extents"
          of a plate are the absolute values of the differences
          between the respective maximum and minimum X, Y, and Z
          coordinates of the plate's vertices.

       Voxel scales determine the resolution of the voxel grid.
       Voxel scales must be chosen to satisfy size constraints and
       provide reasonable plate lookup performance.

       The following considerations apply to spatial indexes of
       type 2 DSK segments:

          1)  The maximum number of coarse voxels is fixed at
              SPICE_DSK02_MAXCGR (declared in SpiceDSK.h).

          2)  If there are too few fine voxels, the average number of
              plates per fine voxel will be very large. This largely
              negates the performance improvement afforded by having an
              index. Also, the number of plates per voxel may exceed
              limits imposed by DSK functions that use static arrays.

          3)  If there are too many fine voxels, the average number of
              voxels intersected by a given plate may be too large for
              all the plate-voxel associations to be stored. In
              addition, the time needed to examine the plate lists for
              each voxel (including the empty ones) may become quite
              large, again negating the value of the index.

       In many cases, voxel scales yielding optimum performance must be
       determined by experiment. However, the following heuristics can
       provide reasonable starting values:

          Let `np' be the number of plates. Let `fs' be the fine voxel
          scale. Then a reasonable value of `fs' may be

                     (0.25)
             fs =  np       / 8.

          In general, `fs' should not smaller than 1.

#### Examples

       The numerical results shown for this example may differ across
       platforms. The results depend on the SPICE kernels used as
       input, the compiler and supporting libraries, and the machine
       specific arithmetic implementation.

       1) Create a three-segment DSK file using plate model data for
          Phobos. Use latitudinal, rectangular, and planetodetic
          coordinates in the respective segments. This is not a
          realistic example, but it serves to demonstrate use of
          the supported coordinate systems.

          Use the DSK kernel below to provide, for simplicity, the
          input plate and vertex data. The selected input file has one
          segment.

             phobos_3_3.bds

          Example code begins here.

          /.
             Program dskmi2_ex1

             Example program for dskw02_c, dskmi2_c, and dskrb2_c

             Create a three-segment DSK file using plate model data for
             Phobos. Use latitudinal, rectangular, and planetodetic
             coordinates in the respective segments.

             For simplicity, use an existing DSK file to provide the
             input plate and vertex data. The selected input file has one
             segment.

                Version 1.0.0 22-JAN-2016 (NJB)

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

          int main()
          {

             /.
             Local constants
             ./
             #define FILSIZ          256
             #define LNSIZE           81
             #define NCOR              4
             #define NSEG              3
             #define NAMLEN           21

             /.
             Local variables
             ./

             /.
             Below, we declare large arrays static to avoid stack
             overflow problems.
             ./

             SpiceBoolean            found;

             SpiceChar               cornam [ NCOR ][ NAMLEN ] =
                                     { "radius",
                                       "Z-coordinate",
                                       "Z-coordinate",
                                       "altitude" };

             SpiceChar             * dsk;
             SpiceChar             * frame;
             SpiceChar             * indsk;

             SpiceDLADescr           dladsc;

             SpiceDouble             corpar [ SPICE_DSK_NSYPAR ];
             SpiceDouble             f;
             SpiceDouble             finscl;
             SpiceDouble             first;
             SpiceDouble             last;
             SpiceDouble             mncor1;
             SpiceDouble             mncor2;
             SpiceDouble             mncor3;
             SpiceDouble             mxcor1;
             SpiceDouble             mxcor2;
             SpiceDouble             mxcor3;
             SpiceDouble             re;
             SpiceDouble             rp;

             /.
             Note: the values of SPICE_DSK02_MAXVRT and
             SPICE_DSK02_MAXPLT declared in SpiceDSK.h,
             integer spatial index dimension SPICE_DSK02_SPAISZ,
             and the workspace dimension SPICE_DSK02_MAXCEL
             are very large. Smaller buffers can be used for most
             applications.
             ./
             static SpiceDouble      spaixd [ SPICE_DSK02_SPADSZ ];
             static SpiceDouble      vrtces [ SPICE_DSK02_MAXVRT ][3];

             SpiceInt                center;
             SpiceInt                corscl;
             SpiceInt                corsys;
             SpiceInt                dclass;
             SpiceInt                handle;
             SpiceInt                i;
             SpiceInt                inhan;
             SpiceInt                np;
             SpiceInt                nv;
             static SpiceInt         plates [ SPICE_DSK02_MAXPLT ][3];
             SpiceInt                segno;
             static SpiceInt         spaixi [ SPICE_DSK02_SPAISZ ];
             SpiceInt                spaisz;
             SpiceInt                surfid;
             SpiceInt                voxpsz;
             SpiceInt                voxlsz;
             static SpiceInt         work   [ SPICE_DSK02_MAXCEL ][2];
             SpiceInt                worksz;

             /.
             Assign names of input and output DSK files.
             ./
             indsk = "phobos_3_3.bds";
             dsk   = "phobos_3_3_3seg.bds";

             /.
             Open input DSK for read access; find first segment.
             ./
             dasopr_c ( indsk, &inhan );
             dlabfs_c ( inhan, &dladsc, &found );

             /.
             Fetch vertices and plates from input DSK file.

             Note that vertex and plate indices are 1-based.
             ./
             printf ( "Reading input data...\n" );

             dskv02_c ( inhan, &dladsc, 1, SPICE_DSK02_MAXVRT,
                        &nv,   vrtces                           );
             dskp02_c ( inhan, &dladsc, 1, SPICE_DSK02_MAXPLT,
                        &np,   plates                           );

             printf ( "Done.\n" );

             /.
             Set input array sizes required by dskmi2_c.
             ./
             voxpsz = SPICE_DSK02_MAXVXP;
             voxlsz = SPICE_DSK02_MXNVLS;
             worksz = SPICE_DSK02_MAXCEL;
             spaisz = SPICE_DSK02_SPAISZ;

             /.
             Set fine and coarse voxel scales. (These usually
             need to determined by experimentation.)
             ./
             finscl = 5.0;
             corscl = 4;

             /.
             Open a new DSK file.
             ./
             dskopn_c ( dsk, dsk, 0, &handle );

             /.
             Create three segments and add them to the file.
             ./
             for ( segno = 1;  segno <= NSEG;  segno++ )
             {
                /.
                Create spatial index. We won't generate a
                vertex-plate mapping, so we set the flag
                for creating this map to "false."
                ./
                printf ( "Creating segment %d\n", (int)segno );
                printf ( "Creating spatial index...\n" );

                dskmi2_c ( nv,     vrtces,     np,     plates,
                           finscl, corscl,     worksz, voxpsz,
                           voxlsz, SPICEFALSE, spaisz, work,
                           spaixd, spaixi                    );

                printf ( "Done.\n" );

                /.
                Set up inputs describing segment attributes:

                - Central body: Phobos
                - Surface ID code: user's choice.
                  We use the segment number here.
                - Data class: general (arbitrary) shape
                - Body-fixed reference frame
                - Time coverage bounds (TBD)
                ./
                center = 401;
                surfid = segno;
                dclass = SPICE_DSK_GENCLS;
                frame  = "IAU_PHOBOS";

                first = -50 * jyear_c();
                last  =  50 * jyear_c();

                /.
                Set the coordinate system and coordinate system
                bounds based on the segment index.

                Zero out the coordinate parameters to start.
                ./
                for ( i = 0;  i < SPICE_DSK_NSYPAR;  i++ )
                {
                   corpar[i] = 0.0;
                }

                if ( segno == 1 )
                {
                   /.
                   Use planetocentric latitudinal coordinates. Set
                   the longitude and latitude bounds.
                   ./
                   corsys = SPICE_DSK_LATSYS;

                   mncor1 = -pi_c();
                   mxcor1 =  pi_c();
                   mncor2 = -pi_c()/2;
                   mxcor2 =  pi_c()/2;
                }
                else if ( segno == 2 )
                {

                   /.
                   Use rectangular coordinates. Set the
                   X and Y bounds.

                   The bounds shown here were derived from
                   the plate data. They lie slightly outside
                   of the range spanned by the plates.
                   ./
                   corsys = SPICE_DSK_RECSYS;

                   mncor1 = -1.3;
                   mxcor1 =  1.31;
                   mncor2 = -1.21;
                   mxcor2 =  1.2;
                }
                else
                {
                   /.
                   Set the coordinate system to planetodetic.
                   ./
                   corsys    = SPICE_DSK_PDTSYS;

                   mncor1    = -pi_c();
                   mxcor1    =  pi_c();
                   mncor2    = -pi_c()/2;
                   mxcor2    =  pi_c()/2;

                   /.
                   We'll use equatorial and polar radii from
                   pck00010.tpc. These normally would be fetched
                   at run time, but for simplicity, we'll use
                   hard-coded values.
                   ./
                   re        = 13.0;
                   rp        =  9.1;
                   f         = ( re - rp ) / re;

                   corpar[0] = re;
                   corpar[1] = f;
                }
                /.
                Compute plate model radius bounds.
                ./
                printf ( "Computing %s bounds of plate set...\n",
                         cornam[corsys-1]                        );

                dskrb2_c ( nv,     vrtces, np,      plates,
                           corsys, corpar, &mncor3, &mxcor3 );

                printf ( "Done.\n" );

                /.
                Write the segment to the file.
                ./
                printf ( "Writing segment...\n" );

                dskw02_c ( handle,
                           center, surfid, dclass, frame,  corsys,
                           corpar, mncor1, mxcor1, mncor2, mxcor2,
                           mncor3, mxcor3, first,  last,   nv,
                           vrtces, np,     plates, spaixd, spaixi );

                printf ( "Done.\n" );
             }

             /.
             Segregate the data records in the DSK file and
             close the file.
             ./
             printf ( "Segregating and closing DSK file...\n" );

             dskcls_c ( handle, SPICETRUE );

             printf ( "Done.\n" );

             return ( 0 );
          }

          When this program was executed on a Mac/Intel/cc/64-bit
          platform, the output was:

          Reading input data...
          Done.
          Creating segment 1
          Creating spatial index...
          Done.
          Computing radius bounds of plate set...
          Done.
          Writing segment...
          Done.
          Creating segment 2
          Creating spatial index...
          Done.
          Computing Z-coordinate bounds of plate set...
          Done.
          Writing segment...
          Done.
          Creating segment 3
          Creating spatial index...
          Done.
          Computing altitude bounds of plate set...
          Done.
          Writing segment...
          Done.
          Segregating and closing DSK file...
          Done.

          Note that after run completion, a new DSK exists in the output
          directory.

#### Restrictions

       None.

#### Literature_References

       None.

#### Author_and_Institution

       N.J. Bachman        (JPL)
       J. Diaz del Rio     (ODC Space)

#### Version

       -CSPICE Version 1.0.1, 10-AUG-2021 (JDR)

           Edited the header to comply with NAIF standard. Fixed I/O type
           of arguments "work", "spaixd" and "spaixi" in -Brief_I/O table.

           Added example's output.

       -CSPICE Version 1.0.0, 13-DEC-2016 (NJB)

#### Index_Entries

       make spatial index for type 2 DSK segment

#### Link to routine dskmi2_c source file dskmi2_c.c

    Fri Dec 31 18:41:04 2021