| dskw02_c |
|
Table of contents
Procedure
dskw02_c ( DSK, write type 2 segment )
void dskw02_c ( SpiceInt handle,
SpiceInt center,
SpiceInt surfid,
SpiceInt dclass,
ConstSpiceChar * frame,
SpiceInt corsys,
ConstSpiceDouble corpar[],
SpiceDouble mncor1,
SpiceDouble mxcor1,
SpiceDouble mncor2,
SpiceDouble mxcor2,
SpiceDouble mncor3,
SpiceDouble mxcor3,
SpiceDouble first,
SpiceDouble last,
SpiceInt nv,
ConstSpiceDouble vrtces[][3],
SpiceInt np,
ConstSpiceInt plates[][3],
ConstSpiceDouble spaixd[],
ConstSpiceInt spaixi[] )
AbstractWrite a type 2 segment to a DSK file. Required_ReadingDAS DSK NAIF_IDS KeywordsDAS DSK FILES PLATE TOPOGRAPHY Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
handle I Handle assigned to the opened DSK file.
center I Central body ID code.
surfid I Surface ID code.
dclass I Data class.
frame I Reference frame.
corsys I Coordinate system code.
corpar I Coordinate system parameters.
mncor1 I Minimum value of first coordinate.
mxcor1 I Maximum value of first coordinate.
mncor2 I Minimum value of second coordinate.
mxcor2 I Maximum value of second coordinate.
mncor3 I Minimum value of third coordinate.
mxcor3 I Maximum value of third coordinate.
first I Coverage start time.
last I Coverage stop time.
nv I Number of vertices.
vrtces I Vertices.
np I Number of plates.
plates I Plates.
spaixd I Double precision component of spatial index.
spaixi I Integer component of spatial index.
SPICE_DSK_ANGMRG
P Angular round-off margin.
SPICE_DSK_GENCLS
P General surface DSK class.
SPICE_DSK_SVFCLS
P Single-valued function DSK class.
SPICE_DSK_NSYPAR
P Maximum number of coordinate system parameters in
a DSK descriptor.
SPICE_DSK02_MAXCGR
P Maximum DSK type 2 coarse voxel count.
SPICE_DSK02_MAXPLT
P Maximum DSK type 2 plate count.
SPICE_DSK02_MAXVOX
P Maximum DSK type 2 voxel count.
SPICE_DSK02_MAXVRT
P Maximum DSK type 2 vertex count.
Detailed_Input
handle is the DAS file handle associated with a DSK file.
The file must be open for write access.
center is the ID code of the body whose surface is described
by the input plate model. `center' refers to an
ephemeris object.
surfid is the ID code of the surface described by the input
plate model. Multiple surfaces (for example, surfaces
having different resolutions) may be associated with a
given body.
dclass is the data class of the input data set. See the
header file SpiceDSK.h for values and meanings.
frame is the name of the reference frame with respect to
which the input data are expressed.
corsys is the coordinate system in which the spatial coverage
of the input data is expressed. `corsys' is an integer
code. See the header file SpiceDSK.h for values and
meanings.
corpar is an array of parameters associated with the input
coordinate system.
For latitudinal and rectangular coordinates, `corpar'
is ignored.
For planetodetic coordinates, the contents of `corpar'
are:
Element Contents
--------- -----------------------------------
corpar[0] Equatorial radius of reference
spheroid.
corpar[1] Flattening coefficient. The polar
radius of the reference spheroid
is given by
corpar[0] * ( 1 - corpar[1] )
corpar[2]...
corpar[SPICE_DSK_NSYPAR-1] Unused.
mncor1,
mxcor1,
mncor2,
mxcor2,
mncor3,
mxcor3 are, respectively, lower and upper bounds of
each of the coordinates of the input data, where the
coordinate system is defined by `corsys' and `corpar'.
These bounds define the region for which the segment
provides data.
Distance units are km. Angular units are radians.
The interpretation of these bounds depends on the data
class; see `dclass' above.
Single-valued surfaces
----------------------
If the segment has data class SPICE_DSK_SVFCLS (see
SpiceDSK.h), the segment defines a surface as a
single-valued function of its domain coordinates:
for example, it may define the radius of the
surface as a function of planetocentric longitude
and latitude.
In this case, the input data must cover a
rectangle in dimensions 1 and 2 of the input
coordinate system: the set of points
R = { (x,y): mncor1 < x < mxcor1;
mncor2 < y < mxcor2 }
must be completely covered by the input data. In
other words, for each point (x,y) of R, there must
be some plate containing a point whose first two
coordinates are (x,y).
The plate set may extend beyond the coordinate
range defined by the bounds on the domain.
Normally for single-valued surfaces, `mncor3' and
`mxcor3' are the minimum and maximum values of the
function attained on the domain.
General surfaces
----------------
If the segment has data class SPICE_DSK_GENCLS (see
SpiceDSK.h), the segment simply contains a collection
of plates: no guarantees are made about the topology
of the surface. The coordinate bounds simply indicate
the spatial region for which the segment provides
data.
Note that shapes of small bodies such as asteroids
and comet nuclei may fall into the "general
surface" category. Surface features such as cliffs,
caves, and arches can prevent a surface from being
represented as a single-valued function of latitude
and longitude, for example.
Longitude interpretation and restrictions
-----------------------------------------
The following rules apply to longitudes provided in
the arguments
mncor1
mxcor1
All angles have units of radians. The tolerance
SPICE_DSK_ANGMRG is used for the comparisons shown
below.
1) Longitudes must be in the range
-2*pi : 2*pi
Values that are out of range by no more than
SPICE_DSK_ANGMRG are bracketed to be in range.
2) It is acceptable for the longitude bounds to be
equal or out of order. If
mxcor1 < mncor1
-
then either `mxcor1' is treated by the DSK
subsystem as though it were mxcor1 + 2*pi, or
`mncor1' is treated as mncor1 - 2*pi: whichever
shift puts the bounds in the allowed range is
made.
The input longitude bounds must not be equal.
If the lower bound is greater than the upper
bound, the difference between the bounds must
not be an integer multiple of 2*pi.
Aside from any small changes made to move the
input values of `mncor1' or `mxcor1' into range,
the values are stored in the DSK segment as is.
3) `mxcor1' must not exceed `mncor1' by more than 2*pi.
Values that are out of range by no more than
SPICE_DSK_ANGMRG are bracketed to be in range.
first,
last are the endpoints of the time interval over which this
data set is applicable. These times are expressed as
seconds past J2000 TDB.
nv is the number of vertices belonging to the plate
model.
vrtces is an array of coordinates of the vertices.
The ith vertex occupies elements [i-1][0:2] of
this array.
np is the number of plates in the plate model.
plates is an array representing the plates of the model.
The elements of `plates' are vertex indices. The vertex
indices of the ith plate occupy elements [i-1][0:2] of
this array.
spaixd,
spaixi are, respectively, the double precision and integer
components of the spatial index of the segment.
It is strongly recommended that the helper routine
dskmi2_c be used to create these arrays. See the
-Examples section below.
Detailed_OutputNone. This routine operates by side effects. Parameters
See the header files
SpiceDSK.h
SpiceDtl.h
for declarations of parameters that may be used as inputs to this
routine, or that may be used to declare bounds of arrays which are
arguments of this routine.
Exceptions
1) If the reference frame name `frame' could not be mapped to
an ID code, the error SPICE(FRAMEIDNOTFOUND) is signaled by
a routine in the call tree of this routine.
2) If the segment stop time precedes the start time, the
error SPICE(TIMESOUTOFORDER) is signaled by a routine in the
call tree of this routine.
3) If an input longitude value is outside the range
[ -2*pi - SPICE_DSK_ANGMRG, 2*pi + SPICE_DSK_ANGMRG ]
the error SPICE(VALUEOUTOFRANGE) is signaled by a routine in
the call tree of this routine. Longitudes outside of the range
by a smaller amount than SPICE_DSK_ANGMRG will be truncated to
lie in the interval [-2*pi, 2*pi].
4) If the absolute value of the difference between the input
maximum longitude and the minimum longitude is more than 2*pi +
SPICE_DSK_ANGMRG, the error SPICE(INVALIDLONEXTENT) will be
signaled by a routine in the call tree of this routine. If
either longitude bound exceeds the other by an amount between
2*pi and 2*pi+SPICE_DSK_ANGMRG, the larger value will be
truncated to the smaller value plus 2*pi.
5) If an input latitude value is outside the range
[ -pi/2 - SPICE_DSK_ANGMRG, pi/2 + SPICE_DSK_ANGMRG ]
the error SPICE(VALUEOUTOFRANGE) is signaled by a routine in
the call tree of this routine. Latitudes outside of the range
by a smaller amount than SPICE_DSK_ANGMRG will be truncated to
lie in the interval [-pi/2, pi/2].
6) If the coordinate system is latitudinal and the lower radius
bound is negative, or if the upper radius bound is
non-positive, the error SPICE(VALUEOUTOFRANGE) is signaled
by a routine in the call tree of this routine.
7) If the coordinate system is latitudinal or planetodetic
and the bounds of the radius or altitude coordinate are
out of order, the error SPICE(BOUNDSOUTOFORDER) is signaled
by a routine in the call tree of this routine.
8) If the coordinate system is latitudinal or planetodetic and
the lower and upper bounds of the longitude, latitude, radius
or altitude coordinate, respectively, are equal, the error
SPICE(ZEROBOUNDSEXTENT) is signaled by a routine in the call
tree of this routine. If the lower longitude bound is greater
than the upper bound, and if the difference between the
bounds is an integer multiple of 2*pi, the same error is
signaled.
9) If the coordinate system is planetodetic and the input
equatorial radius is non-positive, the error
SPICE(VALUEOUTOFRANGE) is signaled by a routine in the call
tree of this routine.
10) If the coordinate system is planetodetic and the input
flattening coefficient is greater than or equal to 1, the
error SPICE(VALUEOUTOFRANGE) is signaled by a routine in the
call tree of this routine.
11) If the coordinate system is planetodetic, and if the minimum
altitude is less than the maximum of
2 2
{ -(B / A), -(A / B) }
where A and B are the semi-major and semi-minor axis lengths
of the reference ellipsoid, the error SPICE(DEGENERATESURFACE)
is signaled by a routine in the call tree of this routine.
12) If the coordinate system is rectangular and any coordinate
lower bound is greater than or equal to the corresponding
upper bound, the error SPICE(BOUNDSOUTOFORDER) is signaled
by a routine in the call tree of this routine.
13) If the coordinate system code is not recognized, the error
SPICE(NOTSUPPORTED) is signaled by a routine in the call tree
of this routine.
14) If any vertex index belonging to an input plate is outside of
the range 1:nv, the error SPICE(BADVERTEXINDEX) is signaled
by a routine in the call tree of this routine.
15) If `nv' is less than 1 or greater than SPICE_DSK02_MAXVRT, the
error SPICE(VALUEOUTOFRANGE) is signaled by a routine in the
call tree of this routine.
16) If `np' is less than 1 or greater than SPICE_DSK02_MAXPLT, the
error SPICE(VALUEOUTOFRANGE) is signaled by a routine in the
call tree of this routine.
17) If any voxel grid extent is less than 1 or greater than
SPICE_DSK02_MAXVOX, the error SPICE(VALUEOUTOFRANGE) is
signaled by a routine in the call tree of this routine.
18) If the voxel count is greater than SPICE_DSK02_MAXVOX, the error
SPICE(VALUEOUTOFRANGE) is signaled by a routine in the call
tree of this routine.
19) If the coarse voxel count is less than 1 or greater than
SPICE_DSK02_MAXCGR, the error SPICE(VALUEOUTOFRANGE) is
signaled by a routine in the call tree of this routine.
20) If the coarse voxel scale is less than 1 or more than
the cube root of the fine voxel count, the error
SPICE(VALUEOUTOFRANGE) is signaled by a routine in the call
tree of this routine.
21) If the cube of the coarse voxel scale does not divide the
fine voxel count evenly, the error SPICE(INCOMPATIBLESCALE)
is signaled by a routine in the call tree of this routine.
22) If the input data class is not recognized, the error
SPICE(NOTSUPPORTED) is signaled by a routine in the call
tree of this routine.
23) If an error occurs while writing the segment to the output
DSK file, the error is signaled by a routine in the call
tree of this routine.
24) If the `frame' input string pointer is null, the error
SPICE(NULLPOINTER) is signaled.
25) If the `frame' input string has zero length, the error
SPICE(EMPTYSTRING) is signaled.
FilesSee argument `handle'. ParticularsThis routine writes a type 2 segment to a DSK file that has been opened for write access. Users planning to create DSK files should consider whether the SPICE DSK creation utility MKDSK may be suitable for their needs. This routine is supported by the routines dskmi2_c and dskrb2_c dskmi2_c simplifies use of this routine by creating the "spatial index" arrays required as inputs by this routine. dskrb2_c computes bounds on the third coordinate of the input plate set. Spatial Indexes =============== 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 subroutines 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 dskw02_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.
RestrictionsNone. Literature_ReferencesNone. Author_and_InstitutionN.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.
Added example's output.
-CSPICE Version 1.0.0, 04-APR-2017 (NJB)
Based on Alpha DSK version 2.0.0, 13-MAY-2010 (NJB).
Caution: this routine's argument list has been changed.
Index_Entrieswrite a type 2 DSK segment |
Fri Dec 31 18:41:05 2021