void gfocce_c ( ConstSpiceChar * occtyp,
ConstSpiceChar * front,
ConstSpiceChar * fshape,
ConstSpiceChar * fframe,
ConstSpiceChar * back,
ConstSpiceChar * bshape,
ConstSpiceChar * bframe,
ConstSpiceChar * abcorr,
ConstSpiceChar * obsrvr,
SpiceDouble tol,
void ( * udstep ) ( SpiceDouble et,
SpiceDouble * step ),
void ( * udrefn ) ( SpiceDouble t1,
SpiceDouble t2,
SpiceBoolean s1,
SpiceBoolean s2,
SpiceDouble * t ),
SpiceBoolean rpt,
void ( * udrepi ) ( SpiceCell * cnfine,
ConstSpiceChar * srcpre,
ConstSpiceChar * srcsuf ),
void ( * udrepu ) ( SpiceDouble ivbeg,
SpiceDouble ivend,
SpiceDouble et ),
void ( * udrepf ) ( void ),
SpiceBoolean bail,
SpiceBoolean ( * udbail ) ( void ),
SpiceCell * cnfine,
SpiceCell * result )
Determine time intervals when an observer sees one target
occulted by another. Report progress and handle interrupts
if so commanded.
FRAMES
GF
KERNEL
NAIF_IDS
SPK
TIME
WINDOWS
EVENT
GEOMETRY
SEARCH
WINDOW
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
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.
tol I Convergence tolerance in seconds.
udstep I Name of the routine that returns a time step.
udrefn I Name of the routine that computes a refined time.
rpt I Progress report flag.
udrepi I Function that initializes progress reporting.
udrepu I Function that updates the progress report.
udrepf I Function that finalizes progress reporting.
bail I Logical indicating program interrupt monitoring.
udbail I Name of a routine that signals a program interrupt.
cnfine I-O SPICE window to which the search is restricted.
result O SPICE window containing results.
occtyp indicates the type of occultation that is to be found.
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 an 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 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".
At least one of the target bodies `front' and `back' must
be modeled as an ellipsoid.
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'. 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 the 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'.
tol is a tolerance value used to determine convergence of
root-finding operations. `tol' is measured in TDB seconds
and must be greater than zero.
udstep is an externally specified routine that computes a
time step in an attempt to find a transition of the
state being considered. In the context of this
routine's algorithm, a "state transition" occurs where
the state changes from being "in occultation" to being
"not in occultation" or vice versa.
This routine relies on `udstep' returning step sizes
small enough so that state transitions within the
confinement window are not overlooked. There must
never be two roots A and B separated by less than
`step', where `step' is the minimum step size returned by
`udstep' for any value of `et'; in the interval [A, B].
The prototype for `udstep' is
void ( * udstep ) ( SpiceDouble et,
SpiceDouble * step )
where:
et is the input start time from which the
algorithm is to search forward for a state
transition. `et' is expressed as seconds past
J2000 TDB.
step is the output step size. `step' indicates
how far to advance `et' so that `et' and
et+step may bracket a state transition and
definitely do not bracket more than one
state transition. Units are TDB seconds.
If a constant step size is desired, the CSPICE routine
gfstep_c
may be used as the step size function. If gfstep_c is
used, the step size must be set by calling gfsstp_c prior
to calling this routine.
udrefn is the name of the externally specified routine that
computes a refinement in the times that bracket a
transition point. In other words, once a pair of
times have been detected such that the system is in
different states at each of the two times, `udrefn'
selects an intermediate time which should be closer to
the transition state than one of the two known times.
The prototype for `udrefn' is:
void ( * udrefn ) ( SpiceDouble t1,
SpiceDouble t2,
SpiceBoolean s1,
SpiceBoolean s2,
SpiceDouble * t )
where the inputs are:
t1 is a time when the system is in state `s1'. `t1'
is expressed as seconds past J2000 TDB.
t2 is a time when the system is in state `s2'. `t2'
is expressed as seconds past J2000 TDB. `t2' is
assumed to be larger than `t1'.
s1 is the state of the system at time t1.
s2 is the state of the system at time t2.
The output is:
t is next time to check for a state transition.
`t' is a number between `t1' and `t2'. `t' is
expressed as seconds past J2000 TDB.
If a simple bisection method is desired, the CSPICE routine
gfrefn_c may be used as the refinement function.
rpt is a logical variable which controls whether
progress reporting is enabled. When `rpt' is SPICETRUE,
progress reporting is enabled and the routines
udrepi, udrepu, and udpref (see descriptions below)
are used to report progress.
udrepi is a user-defined subroutine that initializes a
progress report. When progress reporting is
enabled, `udrepi' is called at the start
of a search. The prototype for `udrefi' is
void ( * udrepi ) ( SpiceCell * cnfine,
ConstSpiceChar * srcpre,
ConstSpiceChar * srcsuf )
where
cnfine
is a confinement window specifying the time period
over which a search is conducted, and
srcpre
srcsuf
are prefix and suffix strings used in the progress
report: these strings are intended to bracket a
representation of the fraction of work done. For
example, when the CSPICE progress reporting functions
are used, if srcpre and srcsuf are, respectively,
"Occultation/transit search"
"done."
the progress report display at the end of
the search will be:
Occultation/transit search 100.00% done.
The CSPICE routine gfrepi_c may be used as the
actual argument corresponding to `udrepi'. If so,
the CSPICE routines gfrepu_c and gfrepf_c must be
the actual arguments corresponding to `udrepu' and
`udrepf'.
udrepu is a user-defined subroutine that updates the
progress report for a search. The prototype
of `udrepu' is
void ( * udrepu ) ( SpiceDouble ivbeg,
SpiceDouble ivend,
SpiceDouble et )
In order for a meaningful progress report to be displayed,
`ivbeg' and `ivend' must satisfy the following constraints:
- `ivbeg' must be less than or equal to `ivend'.
- Over a search, the sum of the differences
ivend - ivbeg
for all calls to this routine made during the search
must equal the measure (that is, the sum of the
lengths of the intervals) of the confinement window
`cnfine'.
`et' is the current time reached in the search for an event.
`et' must lie in the interval
ivbeg : ivend
inclusive. The input values of `et' for a given interval
need not form an increasing sequence.
The CSPICE routine gfrepu_c may be used as the actual
argument corresponding to `udrepu'. If so, the CSPICE
routines gfrepi_c and gfrepf_c must be the actual
arguments corresponding to `udrepi' and `udrepf'.
udrepf is a user-defined subroutine that finalizes a progress
report. `udrepf' has no arguments.
The CSPICE routine gfrepf_c may be used as the actual
argument corresponding to `udrepf'. If so, the CSPICE
routines gfrepi_c and gfrepu_c must be the actual
arguments corresponding to `udrepi' and `udrepu'.
bail is a logical variable indicating whether or not
interrupt handling is enabled. When `bail' is
set to SPICETRUE, the input function `udbail' (see
description below) is used to determine whether
an interrupt has been issued.
udbail is the name of a user defined logical function that
indicates whether an interrupt signal has been
issued (for example, from the keyboard). udbail
has the prototype
SpiceBoolean ( * udbail ) ( void )
The return value is SPICETRUE if an interrupt has
been issued; otherwise the value is SPICEFALSE.
gfocce_c uses `udbail' only when `bail' (see above) is set
to SPICETRUE, indicating that interrupt handling is
enabled. When interrupt handling is enabled, gfocce_c
and routines in its call tree will call `udbail' to
determine whether to terminate processing and return
immediately.
If the user doesn't wish to provide a custom interrupt
handling function, the CSPICE routine
gfbail_c
may be used.
The function `udbail' will be usually be tested
multiple times by the GF system between the time
an interrupt is issued and the time when
control is returned to the calling program, so
`udbail' nmust continue to return SPICETRUE
until explicitly reset by the calling application.
So `udbail' must provide a "reset" mechanism."
In the case of gfbail_c, the reset function is
gfclrh_c
If interrupt handing is not enabled, a logical
function must still be passed to gfocce_c as
an input argument. The CSPICE function
gfbail_c
may be used for this purpose.
See the Examples header section below for a complete code
example demonstrating use of the CSPICE interrupt
handling capability.
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 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 period, when the
specified occultation occurs.
The endpoints of the time intervals comprising `result'
are interpreted as seconds past J2000 TDB.
If `result' is non-empty on input, its contents
will be discarded before gfocce_c conducts its
search.
None.
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, the error
SPICE(INVALIDSTEPSIZE) will be signaled.
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, the error will be diagnosed 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, the error will be diagnosed 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', the error will be diagnosed by a
routine in the call tree of this routine.
6) If the body designated by `front' coincides with that
designated by `back', the error will be diagnosed by a routine
in the call tree of this routine.
7) If either of the body model specifiers `fshape' or `bshape'
is not recognized, the error will be diagnosed by a routine
in the call tree of this routine.
8) If both of the body model specifiers `fshape' and `bshape'
specify point targets, the error will be diagnosed by a
routine in the call tree of this routine.
9) If a target body-fixed reference frame associated with a
non-point target is not recognized, the error will be
diagnosed by a routine in the call tree of this routine.
10) If a target body-fixed reference frame is not centered at
the corresponding target body, the error will be
diagnosed by a routine in the call tree of this routine.
11) If the loaded kernels provide insufficient data to
compute the requested state vector, the deficiency will
be diagnosed by a routine in the call tree of this routine.
12) If an error occurs while reading an SPK or other kernel file,
the error will be diagnosed by a routine in the call tree
of this routine.
13) If the output SPICE window `result' has insufficient capacity
to contain the number of intervals on which the specified
occultation condition is met, the error will be diagnosed
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", the
error will be diagnosed by a routine in the call tree
of this routine.
15) If any input string argument pointer is null, the error
SPICE(NULLPOINTER) will be signaled.
16) If any input string argument, other than `fframe' or `bframe',
is empty, the error SPICE(EMPTYSTRING) will be signaled.
17) If the convergence tolerance size is non-positive, the error
SPICE(INVALIDTOLERANCE) will be signaled.
18) If the occultation type is not recognized, the error
SPICE(INVALIDOCCTYPE) is signaled.
19) If any attempt to change the handler for the interrupt
signal SIGINT fails, the error SPICE(SIGNALFAILURE) is
signaled.
20) If operation of this routine is interrupted, the output result
window will be invalid.
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 target, source and observer that cover the time
period specified by the window `cnfine'. If aberration
corrections are used, the states of target and 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.
In all cases, kernel data are normally loaded once per program
run, NOT every time this routine is called.
This routine provides the SPICE GF system's most flexible
interface for searching for occultation events.
Applications that require do not require support for progress
reporting, interrupt handling, non-default step or refinement
functions, or non-default convergence tolerance normally should
call gfoclt_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 an interval, samples 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 high-level GF routines
that call this routine is set via the parameter SPICE_GF_CNVTOL,
which is declared in the header file SpiceGF.h.
The value of SPICE_GF_CNVTOL is set to a "tight" value so that the
tolerance doesn't become the limiting factor in the accuracy of
solutions found by this routine. In general the accuracy of input
data will be the limiting factor.
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 affect 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. However, the confinement
window can, in some cases, 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. For an example, see the program CASCADE in the GF
Example Programs chapter of the GF Required Reading, gf.req.
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) Conduct a search using default GF progress reporting
and interrupt handling capabilities.
The program will use console I/O to display a simple
ASCII-based progress report.
The program will trap keyboard interrupts (on most systems,
generated by typing the "control C" key combination). This
feature can be used in non-trivial applications to allow
the application to continue after a search as been interrupted.
The program will find occultations of the Sun by the Moon 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 20 seconds, which implies we ignore
occultation events lasting less than 20 seconds, if any exist.
Given this step size and the length of the search interval, the
user has time to interrupt the computation. In an interactive
setting, the user might speed up the search by lengthening the
step size or shortening the search interval, as long as these
adjustments don't prevent the search from finding the correct
solution.
Use the meta-kernel shown below to load the required SPICE
kernels.
KPL/MK
File name: standard.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.
\begindata
KERNELS_TO_LOAD = ( 'de421.bsp',
'pck00008.tpc',
'naif0009.tls' )
\begintext
Example code begins here.
#include "SpiceUsr.h"
#include <stdio.h>
int main()
{
/.
Constants
./
#define TIMFMT "YYYY MON DD HR:MN:SC.###### ::TDB (TDB)"
#define CNVTOL 1.e-6
#define MAXWIN 200
#define TIMLEN 41
/.
Local variables
./
SpiceBoolean bail;
SpiceBoolean rpt;
SpiceChar * win0;
SpiceChar * win1;
SpiceChar begstr [ TIMLEN ];
SpiceChar endstr [ TIMLEN ];
SPICEDOUBLE_CELL ( cnfine, MAXWIN );
SPICEDOUBLE_CELL ( result, MAXWIN );
SpiceDouble et0;
SpiceDouble et1;
SpiceDouble left;
SpiceDouble right;
SpiceInt i;
/.
Load kernels.
./
furnsh_c ( "standard.tm" );
/.
Obtain the TDB time bounds of the confinement
window, which is a single interval in this case.
./
win0 = "2001 DEC 10 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 twenty-second step. We'll ignore any occultations
lasting less than 20 seconds.
./
gfsstp_c ( 20.0 );
/.
Turn on interrupt handling and progress reporting.
./
bail = SPICETRUE;
rpt = SPICETRUE;
/.
Perform the search.
./
gfocce_c ( "ANY",
"MOON", "ellipsoid", "IAU_MOON",
"SUN", "ellipsoid", "IAU_SUN",
"LT", "EARTH", CNVTOL,
gfstep_c, gfrefn_c, rpt,
gfrepi_c, gfrepu_c, gfrepf_c,
bail, gfbail_c, &cnfine,
&result );
if ( gfbail_c() )
{
/.
Clear the CSPICE interrupt indication. This is
an essential step for programs that continue
running after an interrupt; gfbail_c will
continue to return SPICETRUE until this step
has been performed.
./
gfclrh_c();
/.
We've trapped an interrupt signal. In a realistic
application, the program would continue operation
from this point. In this simple example, we simply
display a message and quit.
./
printf ( "\nSearch was interrupted.\n\nThis message "
"was written after an interrupt signal\n"
"was trapped. By default, the program "
"would have terminated \nbefore this message "
"could be written.\n\n" );
}
else
{
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 %ld\n", i );
printf ( " Start time: %s\n", begstr );
printf ( " Stop time: %s\n", endstr );
}
}
}
return ( 0 );
}
When this program was executed on a PC/Linux/gcc platform, the
progress report had the format shown below:
Occultation/transit search 6.02% done.
The completion percentage was updated approximately once per
second.
When this program completed execution, the output was:
Occultation/transit search 100.00% done.
interval 0
start time: 2001 DEC 14 20:10:14.195952 (TDB)
stop time: 2001 DEC 14 21:35:50.317994 (TDB)
When the program was interrupted at an arbitrary time,
the output was:
Occultation/transit search 13.63% done.
Search was interrupted.
This message was written after an interrupt signal
was trapped. By default, the program would have terminated
before this message could be written.
1) If the caller passes in the default, constant step
size routine, gfstep_c, the caller must set the step
size by calling the entry point gfsstp_c before
calling gfocce_c. The call syntax for gfsstp_c is
gfsstp_c ( step );
None.
N.J. Bachman (JPL)
L.S. Elson (JPL)
W.L. Taber (JPL)
I.M. Underwood (JPL)
E.D. Wright (JPL)
-CSPICE Version 1.0.0, 15-APR-2009 (NJB) (LSE) (WLT) (IMU) (EDW )
GF mid-level occultation search
Link to routine gfocce_c source file gfocce_c.c
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