| gfoclt_c |
|
Table of contents
Procedure
gfoclt_c ( GF, find occultation )
void gfoclt_c ( ConstSpiceChar * occtyp,
ConstSpiceChar * front,
ConstSpiceChar * fshape,
ConstSpiceChar * fframe,
ConstSpiceChar * back,
ConstSpiceChar * bshape,
ConstSpiceChar * bframe,
ConstSpiceChar * abcorr,
ConstSpiceChar * obsrvr,
SpiceDouble step,
SpiceCell * cnfine,
SpiceCell * result )
AbstractDetermine time intervals when an observer sees one target occulted by, or in transit across, another. The surfaces of the target bodies may be represented by triaxial ellipsoids or by topographic data provided by DSK files. Required_ReadingFRAMES GF KERNEL NAIF_IDS SPK TIME WINDOWS KeywordsEVENT GEOMETRY SEARCH WINDOW Brief_I/O
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
SPICE_GF_CNVTOL
P Convergence tolerance.
occtyp I Type of occultation.
front I Name of body occulting the other.
fshape I Type of shape model used for front body.
fframe I Body-fixed, body-centered frame for front body.
back I Name of body occulted by the other.
bshape I Type of shape model used for back body.
bframe I Body-fixed, body-centered frame for back body.
abcorr I Aberration correction flag.
obsrvr I Name of the observing body.
step I Step size in seconds for finding occultation
events.
cnfine I-O SPICE window to which the search is restricted.
result O SPICE window containing results.
Detailed_Input
occtyp indicates the type of occultation that is to be found.
Note that transits are considered to be a type of
occultation.
Supported values and corresponding definitions are:
"FULL" denotes the full occultation of the
body designated by `back' by the body
designated by `front', as seen from the
location of the observer. In other
words, the occulted body is completely
invisible as seen from the observer's
location.
"ANNULAR" denotes an annular occultation: the
body designated by `front' blocks part
of, but not the limb of, the body
designated by `back', as seen from the
location of the observer.
"PARTIAL" denotes a partial, non-annular
occultation: the body designated by
`front' blocks part, but not all, of the
limb of the body designated by `back', as
seen from the location of the observer.
"ANY" denotes any of the above three types of
occultations: "PARTIAL", "ANNULAR", or
"FULL".
"ANY" should be used to search for
times when the body designated by `front'
blocks any part of the body designated
by `back'.
The option "ANY" must be used if either
the front or back target body is
modeled as a point.
Case and leading or trailing blanks are not
significant in the string `occtyp'.
front is the name of the target body that occults---that is,
passes in front of---the other. Optionally, you may
supply the integer NAIF ID code for the body as a
string. For example both "MOON" and "301" are
legitimate strings that designate the Moon.
Case and leading or trailing blanks are not
significant in the string `front'.
fshape is a string indicating the geometric model used to
represent the shape of the front target body. The
supported options are:
"ELLIPSOID"
Use a triaxial ellipsoid model with radius
values provided via the kernel pool. A kernel
variable having a name of the form
BODYnnn_RADII
where nnn represents the NAIF integer code
associated with the body, must be present in
the kernel pool. This variable must be
associated with three numeric values giving the
lengths of the ellipsoid's X, Y, and Z
semi-axes.
"POINT"
Treat the body as a single point. When a point
target is specified, the occultation type must
be set to "ANY".
"DSK/UNPRIORITIZED[/SURFACES = <surface list>]"
Use topographic data provided by DSK files to
model the body's shape. These data must be
provided by loaded DSK files.
The surface list specification is optional. The
syntax of the list is
<surface 1> [, <surface 2>...]
If present, it indicates that data only for the
listed surfaces are to be used; however, data
need not be available for all surfaces in the
list. If absent, loaded DSK data for any surface
associated with the target body are used.
The surface list may contain surface names or
surface ID codes. Names containing blanks must
be delimited by double quotes, for example
SURFACES = "Mars MEGDR 128 PIXEL/DEG"
If multiple surfaces are specified, their names
or IDs must be separated by commas.
See the -Particulars section below for details
concerning use of DSK data.
The combinations of the shapes of the target bodies
`front' and `back' must be one of:
One ELLIPSOID, one POINT
Two ELLIPSOIDs
One DSK, one POINT
Case and leading or trailing blanks are not
significant in the string `fshape'.
fframe is the name of the body-fixed, body-centered reference
frame associated with the front target body. Examples of
such names are "IAU_SATURN" (for Saturn) and "ITRF93"
(for the Earth).
If the front target body is modeled as a point, `fframe'
should be left empty or blank.
Case and leading or trailing blanks bracketing a
non-blank frame name are not significant in the string
`fframe'.
back is the name of the target body that is occulted
by---that is, passes in back of---the other.
Optionally, you may supply the integer NAIF ID code
for the body as a string. For example both "MOON" and
"301" are legitimate strings that designate the Moon.
Case and leading or trailing blanks are not
significant in the string `back'.
bshape is the shape specification for the body designated
by `back'. The supported options are those for
`fshape'. See the description of `fshape' above for
details.
bframe is the name of the body-fixed, body-centered reference
frame associated with the ``back'' target body. Examples
of such names are "IAU_SATURN" (for Saturn) and "ITRF93"
(for the Earth).
If the back target body is modeled as a point, `bframe'
should be left empty or blank.
Case and leading or trailing blanks bracketing a
non-blank frame name are not significant in the string
`bframe'.
abcorr indicates the aberration corrections to be applied to
the state of each target body to account for one-way
light time. Stellar aberration corrections are
ignored if specified, since these corrections don't
improve the accuracy of the occultation determination.
See the header of the SPICE routine spkezr_c for a
detailed description of the aberration correction
options. For convenience, the options supported by
this routine are listed below:
"NONE" Apply no correction.
"LT" "Reception" case: correct for
one-way light time using a Newtonian
formulation.
"CN" "Reception" case: converged
Newtonian light time correction.
"XLT" "Transmission" case: correct for
one-way light time using a Newtonian
formulation.
"XCN" "Transmission" case: converged
Newtonian light time correction.
Case and blanks are not significant in the string
`abcorr'.
obsrvr is the name of the body from which the occultation is
observed. Optionally, you may supply the integer NAIF
ID code for the body as a string.
Case and leading or trailing blanks are not
significant in the string `obsrvr'.
step is the step size to be used in the search. `step' must
be shorter than any interval, within the confinement
window, over which the specified occultation condition
is met. In other words, `step' must be shorter than the
shortest occultation event that the user wishes to
detect; `step' must also be shorter than the shortest
time interval between two occultation events that
occur within the confinement window (see below).
However, `step' must not be *too* short, or the search
will take an unreasonable amount of time.
The choice of `step' affects the completeness but not
the precision of solutions found by this routine; the
precision is controlled by the convergence tolerance.
See the discussion of the parameter SPICE_GF_CNVTOL for
details.
`step' has units of TDB seconds.
cnfine is a SPICE window that confines the time period over
which the specified search is conducted. `cnfine' may
consist of a single interval or a collection of
intervals.
The endpoints of the time intervals comprising `cnfine'
are interpreted as seconds past J2000 TDB.
See the -Examples section below for a code example
that shows how to create a confinement window.
`cnfine' must be declared as a double precision SpiceCell.
CSPICE provides the following macro, which declares and
initializes the cell
SPICEDOUBLE_CELL ( cnfine, CNFINESZ );
where CNFINESZ is the maximum capacity of `cnfine'.
Detailed_Output
cnfine is the input confinement window, updated if necessary so the
control area of its data array indicates the window's size
and cardinality. The window data are unchanged.
result is a SPICE window representing the set of time intervals,
within the confinement window, when the specified
occultation occurs.
`result' must be declared and initialized with sufficient
size to capture the full set of time intervals within the
search region on which the specified condition is satisfied.
If `result' is non-empty on input, its contents will be
discarded before gfoclt_c conducts its search.
The endpoints of the time intervals comprising `result' are
interpreted as seconds past J2000 TDB.
If no times within the confinement window satisfy the
search criteria, `result' will be returned with a
cardinality of zero.
`result' must be declared as a double precision SpiceCell.
CSPICE provides the following macro, which declares and
initializes the cell
SPICEDOUBLE_CELL ( result, RESULTSZ );
where RESULTSZ is the maximum capacity of `result'.
Parameters
SPICE_GF_CNVTOL
is the convergence tolerance used for finding endpoints
of the intervals comprising the result window.
SPICE_GF_CNVTOL is used to determine when binary searches
for roots should terminate: when a root is bracketed
within an interval of length SPICE_GF_CNVTOL, the root is
considered to have been found.
The accuracy, as opposed to precision, of roots found
by this routine depends on the accuracy of the input
data. In most cases, the accuracy of solutions will be
inferior to their precision.
SPICE_GF_CNVTOL is declared in the header file
SpiceGF.h
Exceptions
1) In order for this routine to produce correct results,
the step size must be appropriate for the problem at hand.
Step sizes that are too large may cause this routine to miss
roots; step sizes that are too small may cause this routine
to run unacceptably slowly and in some cases, find spurious
roots.
This routine does not diagnose invalid step sizes, except that
if the step size is non-positive, an error is signaled by a
routine in the call tree of this routine.
2) Due to numerical errors, in particular,
- Truncation error in time values
- Finite tolerance value
- Errors in computed geometric quantities
it is *normal* for the condition of interest to not always be
satisfied near the endpoints of the intervals comprising the
result window.
The result window may need to be contracted slightly by the
caller to achieve desired results. The SPICE window routine
wncond_c can be used to contract the result window.
3) If name of either target or the observer cannot be translated
to a NAIF ID code, an error is signaled by a routine
in the call tree of this routine.
4) If the radii of a target body modeled as an ellipsoid cannot
be determined by searching the kernel pool for a kernel
variable having a name of the form
"BODYnnn_RADII"
where nnn represents the NAIF integer code associated with
the body, an error is signaled by a routine in the
call tree of this routine.
5) If either of the target bodies `front' or `back' coincides with
the observer body `obsrvr', an error is signaled by a
routine in the call tree of this routine.
6) If the body designated by `front' coincides with that
designated by `back', an error is signaled by a routine
in the call tree of this routine.
7) If either of the body model specifiers `fshape' or `bshape'
is not recognized, an error is signaled by a routine
in the call tree of this routine.
8) If both of the body model specifiers `fshape' and `bshape'
specify point targets, an error is signaled by a
routine in the call tree of this routine.
9) If one of the body model specifiers `fshape' and `bshape'
specifies a DSK model, and the other argument does not
specify a point target, an error is signaled by a routine in
the call tree of this routine.
10) If a target body-fixed reference frame associated with a
non-point target is not recognized, an error is signaled by a
routine in the call tree of this routine.
11) If a target body-fixed reference frame is not centered at the
corresponding target body, an error is signaled by a routine
in the call tree of this routine.
12) If the loaded kernels provide insufficient data to compute any
required state vector, an error is signaled by a routine in
the call tree of this routine.
13) If an error occurs while reading an SPK or other kernel file,
the error is signaled by a routine in the call tree
of this routine.
14) If a point target is specified and the occultation type is set
to a valid value other than "ANY", an error is signaled by a
routine in the call tree of this routine.
15) If the output SPICE window `result' has size less than 2, the
error SPICE(WINDOWTOOSMALL) is signaled by a routine in the
call tree of this routine.
16) If the output SPICE window `result' has insufficient capacity
to contain the number of intervals on which the specified
occultation condition is met, an error is signaled
by a routine in the call tree of this routine.
17) If the occultation type `occtyp' is invalid, an error is
signaled by a routine in the call tree of this routine.
18) If the aberration correction specification `abcorr' is invalid,
an error is signaled by a routine in the call tree of this
routine.
19) If either `fshape' or `bshape' specifies that the target surface
is represented by DSK data, and no DSK files are loaded for
the specified target, an error is signaled by a routine in
the call tree of this routine.
20) If either `fshape' or `bshape' specifies that the target surface
is represented by DSK data, but the shape specification is
invalid, an error is signaled by a routine in the call tree
of this routine.
21) If any of the `occtyp', `front', `fshape', `back', `bshape',
`abcorr', `obsrvr', `bframe' or `fframe' input string pointers
is null, the error SPICE(NULLPOINTER) is signaled.
22) If any of the `occtyp', `front', `fshape', `back', `bshape',
`abcorr' or `obsrvr' input strings has zero length, the error
SPICE(EMPTYSTRING) is signaled.
23) If any the `cnfine' or `result' cell arguments has a type
other than SpiceDouble, the error SPICE(TYPEMISMATCH) is
signaled.
Files
Appropriate SPICE kernels must be loaded by the calling program
before this routine is called.
The following data are required:
- SPK data: the calling application must load ephemeris data
for the targets, source and observer that cover the time
period specified by the window `cnfine'. If aberration
corrections are used, the states of the target bodies and of
the observer relative to the solar system barycenter must be
calculable from the available ephemeris data. Typically
ephemeris data are made available by loading one or more SPK
files via furnsh_c.
- PCK data: bodies modeled as triaxial ellipsoids must have
semi-axis lengths provided by variables in the kernel pool.
Typically these data are made available by loading a text
PCK file via furnsh_c.
- FK data: if either of the reference frames designated by
`bframe' or `fframe' are not built in to the SPICE system,
one or more FKs specifying these frames must be loaded.
The following data may be required:
- DSK data: if either `fshape' or `bshape' indicates that DSK
data are to be used, DSK files containing topographic data
for the target body must be loaded. If a surface list is
specified, data for at least one of the listed surfaces must
be loaded.
- Surface name-ID associations: if surface names are specified
in `fshape' or `bshape', the association of these names with
their corresponding surface ID codes must be established by
assignments of the kernel variables
NAIF_SURFACE_NAME
NAIF_SURFACE_CODE
NAIF_SURFACE_BODY
Normally these associations are made by loading a text
kernel containing the necessary assignments. An example
of such a set of assignments is
NAIF_SURFACE_NAME += 'Mars MEGDR 128 PIXEL/DEG'
NAIF_SURFACE_CODE += 1
NAIF_SURFACE_BODY += 499
- CK data: either of the body-fixed frames to which `fframe' or
`bframe' refer might be a CK frame. If so, at least one CK
file will be needed to permit transformation of vectors
between that frame and the J2000 frame.
- SCLK data: if a CK file is needed, an associated SCLK
kernel is required to enable conversion between encoded SCLK
(used to time-tag CK data) and barycentric dynamical time
(TDB).
Kernel data are normally loaded once per program run, NOT every
time this routine is called.
ParticularsThis routine provides a simpler, but less flexible, interface than does the CSPICE routine gfocce_c for conducting searches for occultation events. Applications that require support for progress reporting, interrupt handling, non-default step or refinement functions, or non-default convergence tolerance should call gfocce_c rather than this routine. This routine determines a set of one or more time intervals within the confinement window when a specified type of occultation occurs. The resulting set of intervals is returned as a SPICE window. Below we discuss in greater detail aspects of this routine's solution process that are relevant to correct and efficient use of this routine in user applications. The Search Process ================== The search for occultations is treated as a search for state transitions: times are sought when the state of the `back' body changes from "not occulted" to "occulted" or vice versa. Step Size ========= Each interval of the confinement window is searched as follows: first, the input step size is used to determine the time separation at which the occultation state will be sampled. Starting at the left endpoint of the interval, samples of the occultation state will be taken at each step. If a state change is detected, a root has been bracketed; at that point, the "root"--the time at which the state change occurs---is found by a refinement process, for example, via binary search. Note that the optimal choice of step size depends on the lengths of the intervals over which the occultation state is constant: the step size should be shorter than the shortest occultation duration and the shortest period between occultations, within the confinement window. Having some knowledge of the relative geometry of the targets and observer can be a valuable aid in picking a reasonable step size. In general, the user can compensate for lack of such knowledge by picking a very short step size; the cost is increased computation time. Note that the step size is not related to the precision with which the endpoints of the intervals of the result window are computed. That precision level is controlled by the convergence tolerance. Convergence Tolerance ===================== Once a root has been bracketed, a refinement process is used to narrow down the time interval within which the root must lie. This refinement process terminates when the location of the root has been determined to within an error margin called the "convergence tolerance." The convergence tolerance used by this routine is set via the parameter SPICE_GF_CNVTOL. The value of SPICE_GF_CNVTOL is set to a "tight" value so that the tolerance doesn't limit the accuracy of solutions found by this routine. In general the accuracy of input data will be the limiting factor. To use a different tolerance value, a lower-level GF routine such as gfocce_c must be called. Making the tolerance tighter than SPICE_GF_CNVTOL is unlikely to be useful, since the results are unlikely to be more accurate. Making the tolerance looser will speed up searches somewhat, since a few convergence steps will be omitted. However, in most cases, the step size is likely to have a much greater effect on processing time than would the convergence tolerance. The Confinement Window ====================== The simplest use of the confinement window is to specify a time interval within which a solution is sought. The confinement window also can be used to restrict a search to a time window over which required data (typically ephemeris data, in the case of occultation searches) are known to be available. In some cases, the confinement window be used to make searches more efficient. Sometimes it's possible to do an efficient search to reduce the size of the time period over which a relatively slow search of interest must be performed. See the "CASCADE" example program in gf.req for a demonstration. Using DSK data ============== DSK loading and unloading ------------------------- DSK files providing data used by this routine are loaded by calling furnsh_c and can be unloaded by calling unload_c or kclear_c. See the documentation of furnsh_c for limits on numbers of loaded DSK files. For run-time efficiency, it's desirable to avoid frequent loading and unloading of DSK files. When there is a reason to use multiple versions of data for a given target body---for example, if topographic data at varying resolutions are to be used---the surface list can be used to select DSK data to be used for a given computation. It is not necessary to unload the data that are not to be used. This recommendation presumes that DSKs containing different versions of surface data for a given body have different surface ID codes. DSK data priority ----------------- A DSK coverage overlap occurs when two segments in loaded DSK files cover part or all of the same domain---for example, a given longitude-latitude rectangle---and when the time intervals of the segments overlap as well. When DSK data selection is prioritized, in case of a coverage overlap, if the two competing segments are in different DSK files, the segment in the DSK file loaded last takes precedence. If the two segments are in the same file, the segment located closer to the end of the file takes precedence. When DSK data selection is unprioritized, data from competing segments are combined. For example, if two competing segments both represent a surface as a set of triangular plates, the union of those sets of plates is considered to represent the surface. Currently only unprioritized data selection is supported. Because prioritized data selection may be the default behavior in a later version of the routine, the UNPRIORITIZED keyword is required in the `fshape' and `bshape' arguments. Syntax of the shape input arguments for the DSK case ---------------------------------------------------- The keywords and surface list in the target shape arguments `bshape' and `fshape' are called "clauses." The clauses may appear in any order, for example "DSK/<surface list>/UNPRIORITIZED" "DSK/UNPRIORITIZED/<surface list>" "UNPRIORITIZED/<surface list>/DSK" The simplest form of the `method' argument specifying use of DSK data is one that lacks a surface list, for example: "DSK/UNPRIORITIZED" For applications in which all loaded DSK data for the target body are for a single surface, and there are no competing segments, the above string suffices. This is expected to be the usual case. When, for the specified target body, there are loaded DSK files providing data for multiple surfaces for that body, the surfaces to be used by this routine for a given call must be specified in a surface list, unless data from all of the surfaces are to be used together. The surface list consists of the string "SURFACES = " followed by a comma-separated list of one or more surface identifiers. The identifiers may be names or integer codes in string format. For example, suppose we have the surface names and corresponding ID codes shown below: Surface Name ID code ------------ ------- "Mars MEGDR 128 PIXEL/DEG" 1 "Mars MEGDR 64 PIXEL/DEG" 2 "Mars_MRO_HIRISE" 3 If data for all of the above surfaces are loaded, then data for surface 1 can be specified by either "SURFACES = 1" or "SURFACES = \"Mars MEGDR 128 PIXEL/DEG\"" Escaped double quotes are used to delimit the surface name because it contains blank characters. To use data for surfaces 2 and 3 together, any of the following surface lists could be used: "SURFACES = 2, 3" "SURFACES = \"Mars MEGDR 64 PIXEL/DEG\", 3" "SURFACES = 2, Mars_MRO_HIRISE" "SURFACES = \"Mars MEGDR 64 PIXEL/DEG\", Mars_MRO_HIRISE" An example of a shape argument that could be constructed using one of the surface lists above is "DSK/UNPRIORITIZED/SURFACES = \"Mars MEGDR 64 PIXEL/DEG\", 3" Examples
The numerical results shown for these examples 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) Find occultations of the Sun by the Moon (that is, solar
eclipses) as seen from the center of the Earth over the month
December, 2001.
Use light time corrections to model apparent positions of Sun
and Moon. Stellar aberration corrections are not specified
because they don't affect occultation computations.
We select a step size of 3 minutes, which means we
ignore occultation events lasting less than 3 minutes,
if any exist.
Use the meta-kernel shown below to load the required SPICE
kernels.
KPL/MK
File name: gfoclt_ex1.tm
This meta-kernel is intended to support operation of SPICE
example programs. The kernels shown here should not be
assumed to contain adequate or correct versions of data
required by SPICE-based user applications.
In order for an application to use this meta-kernel, the
kernels referenced here must be present in the user's
current working directory.
The names and contents of the kernels referenced
by this meta-kernel are as follows:
File name Contents
--------- --------
de421.bsp Planetary ephemeris
pck00008.tpc Planet orientation and
radii
naif0009.tls Leapseconds
\begindata
KERNELS_TO_LOAD = ( 'de421.bsp',
'pck00008.tpc',
'naif0009.tls' )
\begintext
End of meta-kernel
Example code begins here.
/.
Program gfoclt_ex1
./
#include <stdio.h>
#include "SpiceUsr.h"
int main()
{
/.
Local constants
./
#define TIMFMT "YYYY MON DD HR:MN:SC.###### (TDB)::TDB"
#define MAXWIN 200
#define TIMLEN 41
/.
Local variables
./
SPICEDOUBLE_CELL ( cnfine, MAXWIN );
SPICEDOUBLE_CELL ( result, MAXWIN );
SpiceChar * win0;
SpiceChar * win1;
SpiceChar begstr [ TIMLEN ];
SpiceChar endstr [ TIMLEN ];
SpiceDouble et0;
SpiceDouble et1;
SpiceDouble left;
SpiceDouble right;
SpiceDouble step;
SpiceInt i;
/.
Load kernels.
./
furnsh_c ( "gfoclt_ex1.tm" );
/.
Obtain the TDB time bounds of the confinement
window, which is a single interval in this case.
./
win0 = "2001 DEC 01 00:00:00 TDB";
win1 = "2002 JAN 01 00:00:00 TDB";
str2et_c ( win0, &et0 );
str2et_c ( win1, &et1 );
/.
Insert the time bounds into the confinement
window.
./
wninsd_c ( et0, et1, &cnfine );
/.
Select a 3-minute step. We'll ignore any occultations
lasting less than 3 minutes. Units are TDB seconds.
./
step = 180.0;
/.
Perform the search.
./
gfoclt_c ( "any",
"moon", "ellipsoid", "iau_moon",
"sun", "ellipsoid", "iau_sun",
"lt", "earth", step,
&cnfine, &result );
if ( wncard_c(&result) == 0 )
{
printf ( "No occultation was found.\n" );
}
else
{
for ( i = 0; i < wncard_c(&result); i++ )
{
/.
Fetch and display each occultation interval.
./
wnfetd_c ( &result, i, &left, &right );
timout_c ( left, TIMFMT, TIMLEN, begstr );
timout_c ( right, TIMFMT, TIMLEN, endstr );
printf ( "Interval %d\n"
" Start time: %s\n"
" Stop time: %s\n",
(int)i, begstr, endstr );
}
}
return ( 0 );
}
When this program was executed on a Mac/Intel/cc/64-bit
platform, the output was:
Interval 0
Start time: 2001 DEC 14 20:10:14.195952 (TDB)
Stop time: 2001 DEC 14 21:35:50.317994 (TDB)
2) Find occultations of Titan by Saturn or of Saturn by
Titan as seen from the center of the Earth over the
last four months of 2008. Model both target bodies as
ellipsoids. Search for every type of occultation.
Use light time corrections to model apparent positions of
Saturn and Titan. Stellar aberration corrections are not
specified because they don't affect occultation computations.
We select a step size of 15 minutes, which means we
ignore occultation events lasting less than 15 minutes,
if any exist.
Use the meta-kernel shown below to load the required SPICE
kernels.
KPL/MK
File name: gfoclt_ex2.tm
This meta-kernel is intended to support operation of SPICE
example programs. The kernels shown here should not be
assumed to contain adequate or correct versions of data
required by SPICE-based user applications.
In order for an application to use this meta-kernel, the
kernels referenced here must be present in the user's
current working directory.
The names and contents of the kernels referenced
by this meta-kernel are as follows:
File name Contents
--------- --------
de421.bsp Planetary ephemeris
sat427.bsp Satellite ephemeris for
Saturn
pck00008.tpc Planet orientation and
radii
naif0009.tls Leapseconds
\begindata
KERNELS_TO_LOAD = ( 'de421.bsp',
'sat427.bsp',
'pck00008.tpc',
'naif0009.tls' )
\begintext
End of meta-kernel
Example code begins here.
/.
Program gfoclt_ex2
./
#include <stdio.h>
#include <string.h>
#include "SpiceUsr.h"
int main()
{
/.
Local constants
./
#define TIMFMT "YYYY MON DD HR:MN:SC.###### (TDB)::TDB"
#define MAXWIN 200
#define TIMLEN 41
#define LNSIZE 81
#define NTYPES 4
/.
Local variables
./
SPICEDOUBLE_CELL ( cnfine, MAXWIN );
SPICEDOUBLE_CELL ( result, MAXWIN );
SpiceChar * back;
SpiceChar * bframe;
SpiceChar * front;
SpiceChar * fframe;
SpiceChar line [ LNSIZE ];
SpiceChar * obsrvr;
SpiceChar * occtyp [ NTYPES ] =
{
"FULL",
"ANNULAR",
"PARTIAL",
"ANY"
};
SpiceChar * templt [ NTYPES ] =
{
"Condition: # occultation of # by #",
"Condition: # occultation of # by #",
"Condition: # occultation of # by #",
"Condition: # occultation of # by #"
};
SpiceChar timstr [ TIMLEN ];
SpiceChar title [ LNSIZE ];
SpiceChar * win0;
SpiceChar * win1;
SpiceDouble et0;
SpiceDouble et1;
SpiceDouble finish;
SpiceDouble start;
SpiceDouble step;
SpiceInt i;
SpiceInt j;
SpiceInt k;
/.
Load kernels.
./
furnsh_c ( "gfoclt_ex2.tm" );
/.
Obtain the TDB time bounds of the confinement
window, which is a single interval in this case.
./
win0 = "2008 SEP 01 00:00:00 TDB";
win1 = "2009 JAN 01 00:00:00 TDB";
str2et_c ( win0, &et0 );
str2et_c ( win1, &et1 );
/.
Insert the time bounds into the confinement
window.
./
wninsd_c ( et0, et1, &cnfine );
/.
Select a 15-minute step. We'll ignore any occultations
lasting less than 15 minutes. Units are TDB seconds.
./
step = 900.0;
/.
The observation location is the Earth.
./
obsrvr = "Earth";
/.
Loop over the occultation types.
./
for ( i = 0; i < NTYPES; i++ )
{
/.
For each type, do a search for both transits of
Titan across Saturn and occultations of Titan by
Saturn.
./
for ( j = 0; j < 2; j++ )
{
if ( j == 0 )
{
front = "TITAN";
fframe = "IAU_TITAN";
back = "SATURN";
bframe = "IAU_SATURN";
}
else
{
front = "SATURN";
fframe = "IAU_SATURN";
back = "TITAN";
bframe = "IAU_TITAN";
}
/.
Perform the search. The target body shapes
are modeled as ellipsoids.
./
gfoclt_c ( occtyp[i],
front, "ellipsoid", fframe,
back, "ellipsoid", bframe,
"lt", obsrvr, step,
&cnfine, &result );
/.
Display the results.
./
printf ( "\n" );
/.
Substitute the occultation type and target
body names into the title string:
./
repmc_c ( templt[i], "#", occtyp[i], LNSIZE, title );
repmc_c ( title, "#", back, LNSIZE, title );
repmc_c ( title, "#", front, LNSIZE, title );
printf ( "%s\n", title );
if ( wncard_c(&result) == 0 )
{
printf ( " Result window is empty: "
"no occultation was found.\n" );
}
else
{
printf ( " Result window start, stop times:\n" );
for ( k = 0; k < wncard_c(&result); k++ )
{
/.
Fetch the endpoints of the kth interval
of the result window.
./
wnfetd_c ( &result, k, &start, &finish );
/.
Call strncpy with a length of 7 to include
a terminating null.
./
strncpy ( line, " # #", 7 );
timout_c ( start, TIMFMT, TIMLEN, timstr );
repmc_c ( line, "#", timstr, LNSIZE, line );
timout_c ( finish, TIMFMT, TIMLEN, timstr );
repmc_c ( line, "#", timstr, LNSIZE, line );
printf ( "%s\n", line );
}
}
/.
We've finished displaying the results of the
current search.
./
}
/.
We've finished displaying the results of the
searches using the current occultation type.
./
}
printf ( "\n" );
return ( 0 );
}
When this program was executed on a Mac/Intel/cc/64-bit
platform, the output was:
Condition: FULL occultation of SATURN by TITAN
Result window is empty: no occultation was found.
Condition: FULL occultation of TITAN by SATURN
Result window start, stop times:
2008 OCT 27 22:08:01.672540 (TDB) 2008 OCT 28 01:05:03.332576 (TDB)
2008 NOV 12 21:21:59.270691 (TDB) 2008 NOV 13 02:06:05.034713 (TDB)
2008 NOV 28 20:49:02.415745 (TDB) 2008 NOV 29 02:13:58.978005 (TDB)
2008 DEC 14 20:05:09.258916 (TDB) 2008 DEC 15 01:44:53.517960 (TDB)
2008 DEC 30 19:00:56.586894 (TDB) 2008 DEC 31 00:42:43.219311 (TDB)
Condition: ANNULAR occultation of SATURN by TITAN
Result window start, stop times:
2008 OCT 19 21:29:20.694709 (TDB) 2008 OCT 19 22:53:34.442728 (TDB)
2008 NOV 04 20:15:38.652650 (TDB) 2008 NOV 05 00:18:59.130645 (TDB)
2008 NOV 20 19:38:59.674043 (TDB) 2008 NOV 21 00:35:26.726756 (TDB)
2008 DEC 06 18:58:34.093679 (TDB) 2008 DEC 07 00:16:17.653066 (TDB)
2008 DEC 22 18:02:46.308375 (TDB) 2008 DEC 22 23:26:52.721881 (TDB)
Condition: ANNULAR occultation of TITAN by SATURN
Result window is empty: no occultation was found.
Condition: PARTIAL occultation of SATURN by TITAN
Result window start, stop times:
2008 OCT 19 20:44:30.377189 (TDB) 2008 OCT 19 21:29:20.694709 (TDB)
2008 OCT 19 22:53:34.442728 (TDB) 2008 OCT 19 23:38:26.219865 (TDB)
2008 NOV 04 19:54:40.368045 (TDB) 2008 NOV 04 20:15:38.652650 (TDB)
2008 NOV 05 00:18:59.130645 (TDB) 2008 NOV 05 00:39:58.607159 (TDB)
2008 NOV 20 19:21:46.714396 (TDB) 2008 NOV 20 19:38:59.674043 (TDB)
2008 NOV 21 00:35:26.726756 (TDB) 2008 NOV 21 00:52:40.606954 (TDB)
2008 DEC 06 18:42:36.120122 (TDB) 2008 DEC 06 18:58:34.093679 (TDB)
2008 DEC 07 00:16:17.653066 (TDB) 2008 DEC 07 00:32:16.331199 (TDB)
2008 DEC 22 17:47:10.796147 (TDB) 2008 DEC 22 18:02:46.308375 (TDB)
2008 DEC 22 23:26:52.721881 (TDB) 2008 DEC 22 23:42:28.860689 (TDB)
Condition: PARTIAL occultation of TITAN by SATURN
Result window start, stop times:
2008 OCT 27 21:37:17.003993 (TDB) 2008 OCT 27 22:08:01.672540 (TDB)
2008 OCT 28 01:05:03.332576 (TDB) 2008 OCT 28 01:35:49.235670 (TDB)
2008 NOV 12 21:01:47.121213 (TDB) 2008 NOV 12 21:21:59.270691 (TDB)
2008 NOV 13 02:06:05.034713 (TDB) 2008 NOV 13 02:26:18.211753 (TDB)
2008 NOV 28 20:31:28.534248 (TDB) 2008 NOV 28 20:49:02.415745 (TDB)
2008 NOV 29 02:13:58.978005 (TDB) 2008 NOV 29 02:31:33.684575 (TDB)
2008 DEC 14 19:48:27.106157 (TDB) 2008 DEC 14 20:05:09.258916 (TDB)
2008 DEC 15 01:44:53.517960 (TDB) 2008 DEC 15 02:01:36.356012 (TDB)
2008 DEC 30 18:44:23.495003 (TDB) 2008 DEC 30 19:00:56.586894 (TDB)
2008 DEC 31 00:42:43.219311 (TDB) 2008 DEC 31 00:59:17.027816 (TDB)
Condition: ANY occultation of SATURN by TITAN
Result window start, stop times:
2008 OCT 19 20:44:30.377189 (TDB) 2008 OCT 19 23:38:26.219865 (TDB)
2008 NOV 04 19:54:40.368045 (TDB) 2008 NOV 05 00:39:58.607159 (TDB)
2008 NOV 20 19:21:46.714396 (TDB) 2008 NOV 21 00:52:40.606954 (TDB)
2008 DEC 06 18:42:36.120122 (TDB) 2008 DEC 07 00:32:16.331199 (TDB)
2008 DEC 22 17:47:10.796147 (TDB) 2008 DEC 22 23:42:28.860689 (TDB)
Condition: ANY occultation of TITAN by SATURN
Result window start, stop times:
2008 OCT 27 21:37:17.003993 (TDB) 2008 OCT 28 01:35:49.235670 (TDB)
2008 NOV 12 21:01:47.121213 (TDB) 2008 NOV 13 02:26:18.211753 (TDB)
2008 NOV 28 20:31:28.534248 (TDB) 2008 NOV 29 02:31:33.684575 (TDB)
2008 DEC 14 19:48:27.106157 (TDB) 2008 DEC 15 02:01:36.356012 (TDB)
2008 DEC 30 18:44:23.495003 (TDB) 2008 DEC 31 00:59:17.027816 (TDB)
3) Find occultations of the Mars Reconnaissance Orbiter (MRO)
by Mars, or transits of the MRO spacecraft across Mars,
as seen from the DSN station DSS-14 over a period of a
few hours on FEB 28 2015.
Use both ellipsoid and DSK shape models for Mars.
Use light time corrections to model apparent positions of Mars
and MRO. Stellar aberration corrections are not specified
because they don't affect occultation computations.
We select a step size of 3 minutes, which means we ignore
occultation events lasting less than 3 minutes, if any exist.
Use the meta-kernel shown below to load the required SPICE
kernels.
KPL/MK
File: gfoclt_ex3.tm
This meta-kernel is intended to support operation of SPICE
example programs. The kernels shown here should not be
assumed to contain adequate or correct versions of data
required by SPICE-based user applications.
In order for an application to use this meta-kernel, the
kernels referenced here must be present in the user's
current working directory.
The names and contents of the kernels referenced
by this meta-kernel are as follows:
File name Contents
--------- --------
de410.bsp Planetary ephemeris
mar063.bsp Mars satellite ephemeris
pck00010.tpc Planet orientation and
radii
naif0011.tls Leapseconds
earthstns_itrf93_050714.bsp DSN station ephemeris
earth_latest_high_prec.bpc Earth orientation
mro_psp34.bsp MRO ephemeris
megr90n000cb_plate.bds Plate model based on
MEGDR DEM, resolution
4 pixels/degree.
\begindata
KERNELS_TO_LOAD = ( 'de410.bsp',
'mar063.bsp',
'mro_psp34.bsp',
'earthstns_itrf93_050714.bsp',
'earth_latest_high_prec.bpc',
'pck00010.tpc',
'naif0011.tls',
'megr90n000cb_plate.bds' )
\begintext
End of meta-kernel
Example code begins here.
/.
Program gfoclt_ex3
./
#include <stdio.h>
#include "SpiceUsr.h"
int main()
{
/.
Local constants
./
#define META "gfoclt_ex3.tm"
#define TIMFMT "YYYY MON DD HR:MN:SC" \
".###### (TDB)::TDB"
#define MAXWIN 200
#define TIMLEN 41
/.
Local variables
./
SPICEDOUBLE_CELL ( cnfine, MAXWIN );
SPICEDOUBLE_CELL ( result, MAXWIN );
SpiceChar * abcorr;
SpiceChar * back;
SpiceChar begstr [ TIMLEN ];
SpiceChar * bframe;
SpiceChar * bshape;
SpiceChar endstr [ TIMLEN ];
SpiceChar * fframe;
SpiceChar * front;
SpiceChar * fshape;
SpiceChar * obsrvr;
SpiceChar * occtyp;
SpiceChar * win0;
SpiceChar * win1;
SpiceDouble et0;
SpiceDouble et1;
SpiceDouble left;
SpiceDouble right;
SpiceDouble step;
SpiceInt i;
SpiceInt j;
SpiceInt k;
/.
Load kernels.
./
furnsh_c ( META );
/.
Set the observer and aberration correction.
./
obsrvr = "DSS-14";
abcorr = "CN";
/.
Set the occultation type.
./
occtyp = "ANY";
/.
Set the TDB time bounds of the confinement
window, which is a single interval in this case.
./
win0 = "2015 FEB 28 07:00:00 TDB";
win1 = "2015 FEB 28 12:00:00 TDB";
str2et_c ( win0, &et0 );
str2et_c ( win1, &et1 );
/.
Insert the time bounds into the confinement
window.
./
wninsd_c ( et0, et1, &cnfine );
/.
Select a 3-minute step. We'll ignore any occultations
lasting less than 3 minutes. Units are TDB seconds.
./
step = 180.0;
/.
Perform both spacecraft occultation and spacecraft
transit searches.
./
for ( i = 0; i < 2; i++ )
{
if ( i == 0 )
{
/.
Perform a spacecraft occultation search.
./
front = "MARS";
fframe = "IAU_MARS";
back = "MRO";
bshape = "POINT";
bframe = " ";
}
else
{
/.
Perform a spacecraft transit search.
./
front = "MRO";
fframe = " ";
fshape = "POINT";
back = "MARS";
bframe = "IAU_MARS";
}
for ( j = 0; j < 2; j++ )
{
if ( j == 0 )
{
/.
Model the planet shape as an ellipsoid.
./
if ( i == 0 )
{
fshape = "ELLIPSOID";
}
else
{
bshape = "ELLIPSOID";
}
}
else
{
/.
Model the planet shape using DSK data.
./
if ( i == 0 )
{
fshape = "DSK/UNPRIORITIZED";
}
else
{
bshape = "DSK/UNPRIORITIZED";
}
}
/.
Perform the spacecraft occultation or
transit search.
./
printf ( "\n" );
if ( i == 0 )
{
printf ( "Using shape model %s\n"
"Starting occultation search...\n",
fshape );
}
else
{
printf ( "Using shape model %s\n"
"Starting transit search...\n",
bshape );
}
gfoclt_c ( occtyp,
front, fshape, fframe,
back, bshape, bframe,
abcorr, obsrvr, step,
&cnfine, &result );
if ( wncard_c(&result) == 0 )
{
printf ( "No event was found.\n" );
}
else
{
for ( k = 0; k < wncard_c(&result); k++ )
{
/.
Fetch and display each occultation interval.
./
wnfetd_c ( &result, k, &left, &right );
timout_c ( left, TIMFMT, TIMLEN, begstr );
timout_c ( right, TIMFMT, TIMLEN, endstr );
printf ( "Interval %d\n"
" Start time: %s\n"
" Stop time: %s\n",
(int)k, begstr, endstr );
}
}
}
/.
End of the target shape loop.
./
}
/.
End of the occultation vs transit loop.
./
printf ( "\n" );
return ( 0 );
}
When this program was executed on a Mac/Intel/cc/64-bit
platform, the output was:
Using shape model ELLIPSOID
Starting occultation search...
Interval 0
Start time: 2015 FEB 28 07:17:35.379879 (TDB)
Stop time: 2015 FEB 28 07:50:37.710284 (TDB)
Interval 1
Start time: 2015 FEB 28 09:09:46.920140 (TDB)
Stop time: 2015 FEB 28 09:42:50.497193 (TDB)
Interval 2
Start time: 2015 FEB 28 11:01:57.845730 (TDB)
Stop time: 2015 FEB 28 11:35:01.489716 (TDB)
Using shape model DSK/UNPRIORITIZED
Starting occultation search...
Interval 0
Start time: 2015 FEB 28 07:17:38.130608 (TDB)
Stop time: 2015 FEB 28 07:50:38.310802 (TDB)
Interval 1
Start time: 2015 FEB 28 09:09:50.314903 (TDB)
Stop time: 2015 FEB 28 09:42:55.369626 (TDB)
Interval 2
Start time: 2015 FEB 28 11:02:01.756296 (TDB)
Stop time: 2015 FEB 28 11:35:08.368384 (TDB)
Using shape model ELLIPSOID
Starting transit search...
Interval 0
Start time: 2015 FEB 28 08:12:21.112018 (TDB)
Stop time: 2015 FEB 28 08:45:48.401746 (TDB)
Interval 1
Start time: 2015 FEB 28 10:04:32.682324 (TDB)
Stop time: 2015 FEB 28 10:37:59.920302 (TDB)
Interval 2
Start time: 2015 FEB 28 11:56:39.757564 (TDB)
Stop time: 2015 FEB 28 12:00:00.000000 (TDB)
Using shape model DSK/UNPRIORITIZED
Starting transit search...
Interval 0
Start time: 2015 FEB 28 08:12:15.750020 (TDB)
Stop time: 2015 FEB 28 08:45:43.406870 (TDB)
Interval 1
Start time: 2015 FEB 28 10:04:29.031706 (TDB)
Stop time: 2015 FEB 28 10:37:55.565509 (TDB)
Interval 2
Start time: 2015 FEB 28 11:56:34.634642 (TDB)
Stop time: 2015 FEB 28 12:00:00.000000 (TDB)
RestrictionsNone. Literature_ReferencesNone. Author_and_InstitutionN.J. Bachman (JPL) J. Diaz del Rio (ODC Space) L.S. Elson (JPL) E.D. Wright (JPL) Version
-CSPICE Version 1.0.2, 25-NOV-2021 (JDR) (NJB)
Edited the header to comply with NAIF standard.
Updated the description of "cnfine" and "result" arguments.
Added entries #9, #15 and #23 in -Exceptions section.
-CSPICE Version 1.0.1, 12-JUL-2016 (NJB) (EDW)
Edit to example program to use "%d" with explicit casts
to int for printing SpiceInts with printf.
Updated to support use of DSKs.
-CSPICE Version 1.0.0, 07-APR-2009 (NJB) (LSE) (EDW)
Index_EntriesGF occultation search |
Fri Dec 31 18:41:07 2021