Table of contents
CSPICE_DSKW02 writes a type 2 DSK segment.
Given:
handle the DAS file handle associated with the file.
help, handle
LONG = Scalar
The file must be open for write access.
center the ID code of the body whose surface is described by the input
plate model.
help, center
LONG = Scalar
`center' refers to an ephemeris object.
surfid the ID code of the surface described by the input plate model.
help, surfid
LONG = Scalar
Multiple surfaces (for example, surfaces having different
resolutions) may be associated with a given body.
dclass the data class of the input data set.
help, dclass
LONG = Scalar
See the header file IcyDSK.pro for values and meanings.
frame the name of the reference frame with respect to which the input
data are expressed.
help, frame
STRING = Scalar
corsys the coordinate system in which the spatial coverage of the input
data is expressed.
help, corsys
LONG = Scalar
`corsys' is an integer code. See the header file IcyDSK.pro for
values and meanings.
corpar an array of parameters associated with the input coordinate
system.
help, corpar
DOUBLE = Array[SPICE_DSK_NSYPAR]
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 respectively, lower and upper bounds of each of the coordinates
of the input data, where the coordinate system is defined by
`corsys' and `corpar'.
help, mncor1
DOUBLE = Scalar
help, mxcor1
DOUBLE = Scalar
help, mncor2
DOUBLE = Scalar
help, mxcor2
DOUBLE = Scalar
help, mncor3
DOUBLE = Scalar
help, mxcor3
DOUBLE = Scalar
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
IcyDSK.pro), 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
IcyDSK.pro), 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 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 the endpoints of the time interval over which this data set is
applicable.
help, first
DOUBLE = Scalar
help, last
DOUBLE = Scalar
These times are expressed as seconds past J2000 TDB.
vrtces an array of coordinates of the vertices.
help, vrtces
DOUBLE = Array[3,NV]
The ith vertex occupies elements [0:2,i-1] of this array.
plates an array representing the plates of the model.
help, plates
LONG = Array[3,NP]
The elements of `plates' are vertex indices. The vertex indices
of the ith plate occupy elements [0:2,i-1] of this array.
spaixd,
spaixi respectively, the double precision and integer components of the
spatial index of the segment.
help, spaixd
DOUBLE = Array[M]
help, spaixi
LONG = Array[N]
It is strongly recommended that the helper routine
cspice_dskmi2 be used to create these arrays. See the
-Examples section below.
the call:
cspice_dskw02, handle, center, surfid, dclass, frame, corsys, corpar, $
mncor1, mxcor1, mncor2, mxcor2, mncor3, mxcor3, $
first, last, vrtces, plates, spaixd, spaixi
returns:
None.
This routine operates by side effects.
See the include files
IcyDSK.pro
IcyDtl.pro
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.
Any numerical results shown for this example may differ between
platforms as the results depend on the SPICE kernels used as input
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 vertices data. This file has one segment only.
phobos_3_3.bds
Example code begins here.
PRO dskw02_ex1
;;
;; IcyUser globally defines DSK parameters.
;; For more information, please see IcyDSK.pro.
;;
@IcyUser
SPICETRUE = 1L
NSEG = 3
cornam = ['radius', 'Z-coordinate', 'Z-coordinate', 'altitude']
;;
;; Assign names of input and output DSK files.
;;
indsk = 'phobos_3_3.bds'
dsk = 'phobos_3_3_3seg.bds'
if ( cspice_exists(dsk) ) then begin
file_delete, dsk
endif
;;
;; Open input DSK for read access; find first segment.
;;
cspice_dasopr, indsk, inhan
cspice_dlabfs, inhan, dladsc, found
;;
;; Fetch vertices and plates from input DSK file.
;;
;; Note that vertex and plate indices are 1-based.
;;
print, 'Reading input data...'
cspice_dskv02, inhan, dladsc, 1, SPICE_DSK02_MAXVRT, vrtces
cspice_dskp02, inhan, dladsc, 1, SPICE_DSK02_MAXPLT, plates
print, 'Done.'
;;
;; Set input array sizes required by cspice_dskmi2.
;;
voxpsz = SPICE_DSK02_MAXVXP
voxlsz = SPICE_DSK02_MXNVLS
worksz = SPICE_DSK02_MAXCEL
spaisz = SPICE_DSK02_SPAISZ
makvtl = SPICETRUE
;;
;; Set fine and coarse voxel scales. (These usually
;; need to determined by experimentation.)
;;
finscl = 5.D
corscl = 4
;;
;; Open a new DSK file.
;;
cspice_dskopn, dsk, dsk, 0, handle
for segno=1, NSEG do begin
;;
;; Create spatial index. We won't generate a
;; vertex-plate mapping, so we set the flag
;; for creating this map to "false."
;;
print, 'Creating segment ', segno
print, 'Creating spatial index...'
cspice_dskmi2, vrtces, plates, finscl, corscl, $
worksz, voxpsz, voxlsz, makvtl, $
spaisz, spaixd, spaixi
print, 'Done.'
;;
;; 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.D * cspice_jyear()
last = 50.D * cspice_jyear()
;;
;; Set the coordinate system and coordinate system
;; bounds based on the segment index.
;;
;; Zero out the coordinate parameters to start.
;;
corpar = dblarr(SPICE_DSK_NSYPAR)
case segno of
1 : begin
;;
;; Use planetocentric latitudinal coordinates. Set
;; the longitude and latitude bounds.
;;
corsys = SPICE_DSK_LATSYS
mncor1 = -cspice_pi()
mxcor1 = cspice_pi()
mncor2 = -cspice_halfpi()
mxcor2 = cspice_halfpi()
end
2 : begin
;;
;; 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 = -1.3D
mxcor1 = 1.31D
mncor2 = -1.21D
mxcor2 = 1.2D
end
3 : begin
;;
;; Set the coordinate system to planetodetic.
;;
corsys = SPICE_DSK_PDTSYS
mncor1 = -cspice_pi()
mxcor1 = cspice_pi()
mncor2 = -cspice_halfpi()
mxcor2 = cspice_halfpi()
;;
;; 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.D0
rp = 9.1D
f = ( re - rp ) / re
corpar = [ re, f ]
end
else: message, 'Icy(BUG)'
endcase
;;
;; Compute plate model radius bounds.
;;
print, 'Computing ' + cornam[corsys-1] +' bounds of plate set...'
cspice_dskrb2, vrtces, plates, corsys, corpar, mncor3, mxcor3
print, 'Done.'
;;
;; Write the segment to the file.
;;
print, 'Writing segment...'
cspice_dskw02, handle, $
center, $
surfid, $
dclass, $
frame, $
corsys, $
corpar, $
mncor1, $
mxcor1, $
mncor2, $
mxcor2, $
mncor3, $
mxcor3, $
first, $
last, $
vrtces, $
plates, $
spaixd, $
spaixi
end
;;
;; Close the input DSK.
;;
cspice_dskcls, handle, SPICETRUE
cspice_dascls, inhan
END
When this program was executed on a Mac/Intel/IDL8.x/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...
Creating segment 2
Creating spatial index...
Done.
Computing Z-coordinate bounds of plate set...
Done.
Writing segment...
Creating segment 3
Creating spatial index...
Done.
Computing altitude bounds of plate set...
Done.
Writing segment...
Note that after run completion, a new DSK exists in the output
directory.
This 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 cspice_dskmi2 and cspice_dskrb2
cspice_dskmi2 simplifies use of this routine by creating the "spatial
index" arrays required as inputs by this routine. cspice_dskrb2 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 IcyDSK.pro).
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.
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 - angmrg, 2*pi + 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 `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
+ angmrg, the error SPICE(INVALIDLONEXTENT) is 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+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 - angmrg, pi/2 + 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 `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 latitude, 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, where `nv' is the number of vertices, the
error SPICE(BADVERTEXINDEX) is signaled by a routine in the
call tree of this routine.
15) If `nv', the number of vertices, 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', the number of plates, 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 any of the input arguments, `handle', `center', `surfid',
`dclass', `frame', `corsys', `corpar', `mncor1', `mxcor1',
`mncor2', `mxcor2', `mncor3', `mxcor3', `first', `last',
`vrtces', `plates', `spaixd' or `spaixi', is undefined, an
error is signaled by the IDL error handling system.
25) If any of the input arguments, `handle', `center', `surfid',
`dclass', `frame', `corsys', `corpar', `mncor1', `mxcor1',
`mncor2', `mxcor2', `mncor3', `mxcor3', `first', `last',
`vrtces', `plates', `spaixd' or `spaixi', is not of the
expected type, or it does not have the expected dimensions and
size, an error is signaled by the Icy interface.
See argument `handle'.
None.
ICY.REQ
DAS.REQ
DSK.REQ
None.
J. Diaz del Rio (ODC Space)
M. Liukis (JPL)
E.D. Wright (JPL)
-Icy Version 1.0.1, 10-AUG-2021 (JDR)
Edited the header to comply with NAIF standard.
Added -Parameters, -Exceptions, -Files, -Restrictions,
-Literature_References and -Author_and_Institution sections.
Removed reference to the routine's corresponding CSPICE header from
-Abstract section.
Added arguments' type and size information in the -I/O section.
-Icy Version 1.0.0, 04-APR-2017 (ML) (EDW)
write a type 2 DSK segment
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