/* -Procedure gfocce_c ( GF, occultation event ) -Abstract Determine time intervals when an observer sees one target occulted by another. Report progress and handle interrupts if so commanded. The surfaces of the target bodies may be represented by triaxial ellipsoids or by topographic data provided by DSK files. -Disclaimer THIS SOFTWARE AND ANY RELATED MATERIALS WERE CREATED BY THE CALIFORNIA INSTITUTE OF TECHNOLOGY (CALTECH) UNDER A U.S. GOVERNMENT CONTRACT WITH THE NATIONAL AERONAUTICS AND SPACE ADMINISTRATION (NASA). THE SOFTWARE IS TECHNOLOGY AND SOFTWARE PUBLICLY AVAILABLE UNDER U.S. EXPORT LAWS AND IS PROVIDED "AS-IS" TO THE RECIPIENT WITHOUT WARRANTY OF ANY KIND, INCLUDING ANY WARRANTIES OF PERFORMANCE OR MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE OR PURPOSE (AS SET FORTH IN UNITED STATES UCC SECTIONS 2312-2313) OR FOR ANY PURPOSE WHATSOEVER, FOR THE SOFTWARE AND RELATED MATERIALS, HOWEVER USED. IN NO EVENT SHALL CALTECH, ITS JET PROPULSION LABORATORY, OR NASA BE LIABLE FOR ANY DAMAGES AND/OR COSTS, INCLUDING, BUT NOT LIMITED TO, INCIDENTAL OR CONSEQUENTIAL DAMAGES OF ANY KIND, INCLUDING ECONOMIC DAMAGE OR INJURY TO PROPERTY AND LOST PROFITS, REGARDLESS OF WHETHER CALTECH, JPL, OR NASA BE ADVISED, HAVE REASON TO KNOW, OR, IN FACT, SHALL KNOW OF THE POSSIBILITY. RECIPIENT BEARS ALL RISK RELATING TO QUALITY AND PERFORMANCE OF THE SOFTWARE AND ANY RELATED MATERIALS, AND AGREES TO INDEMNIFY CALTECH AND NASA FOR ALL THIRD-PARTY CLAIMS RESULTING FROM THE ACTIONS OF RECIPIENT IN THE USE OF THE SOFTWARE. -Required_Reading FRAMES GF KERNEL NAIF_IDS SPK TIME WINDOWS -Keywords EVENT GEOMETRY SEARCH WINDOW */ #include #include "SpiceUsr.h" #include "SpiceZmc.h" #include "SpiceZfc.h" #include "SpiceZad.h" 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 ) /* -Brief_I/O 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. -Detailed_Input 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 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 = ]" 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 [, ...] 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'. 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. -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 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. -Parameters None. -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, 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) Invalid aberration correction specifications will be diagnosed by a routine in the call tree of this routine. 16) 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, the error is signaled by a routine in the call tree of this routine. 17) If either `fshape' or `bshape' specifies that the target surface is represented by DSK data, but the shape specification is invalid, the error is signaled by a routine in the call tree of this routine. 18) If any input string argument pointer is null, the error SPICE(NULLPOINTER) will be signaled. 19) If any input string argument, other than `fframe' or `bframe', is empty, the error SPICE(EMPTYSTRING) will be signaled. 20) If the convergence tolerance size is non-positive, the error SPICE(INVALIDTOLERANCE) will be signaled. 21) If the occultation type is not recognized, the error SPICE(INVALIDOCCTYPE) is signaled. 22) If any attempt to change the handler for the interrupt signal SIGINT fails, the error SPICE(SIGNALFAILURE) is signaled. 23) If operation of this routine is interrupted, the output result window will be invalid. -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. -Particulars 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. 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//UNPRIORITIZED" "DSK/UNPRIORITIZED/" "UNPRIORITIZED//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) 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 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 %d\n", (int)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. -Restrictions 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 ); -Literature_References None. -Author_and_Institution N.J. Bachman (JPL) L.S. Elson (JPL) W.L. Taber (JPL) I.M. Underwood (JPL) E.D. Wright (JPL) -Version -CSPICE Version 2.0.0, 29-FEB-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, 15-APR-2009 (NJB) (LSE) (WLT) (IMU) (EDW) -Index_Entries GF mid-level occultation search -& */ { /* Begin gfocce_c */ /* Prototypes */ void ( * defSigHandler ) (int); void ( * sigPtr ) (int); /* Local variables */ logical interrupt; logical rep; SpiceBoolean newHandler; static const SpiceChar * blankStr = " "; SpiceChar * bFrameStr; SpiceChar * fFrameStr; /* Participate in error tracing. */ if ( return_c() ) { return; } chkin_c ( "gfocce_c" ); /* Make sure cell data types are d.p. */ CELLTYPECHK2 ( CHK_STANDARD, "gfocce_c", SPICE_DP, cnfine, result ); /* Initialize the input cells if necessary. */ CELLINIT2 ( cnfine, result ); /* The input frame names are special cases because we allow the caller to pass in empty strings. If either of these strings are empty, we pass a null-terminated string containing one blank character to the underlying f2c'd routine. First make sure the frame name pointers are non-null. */ CHKPTR ( CHK_STANDARD, "gfocce_c", bframe ); CHKPTR ( CHK_STANDARD, "gfocce_c", fframe ); /* Use the input frame strings if they're non-empty; otherwise use blank strings for the frame names. */ if ( bframe[0] ) { bFrameStr = (SpiceChar *) bframe; } else { bFrameStr = (SpiceChar *) blankStr; } if ( fframe[0] ) { fFrameStr = (SpiceChar *) fframe; } else { fFrameStr = (SpiceChar *) blankStr; } /* Check the other input strings to make sure each pointer is non-null and each string length is non-zero. */ CHKFSTR ( CHK_STANDARD, "gfocce_c", occtyp ); CHKFSTR ( CHK_STANDARD, "gfocce_c", front ); CHKFSTR ( CHK_STANDARD, "gfocce_c", fshape ); CHKFSTR ( CHK_STANDARD, "gfocce_c", back ); CHKFSTR ( CHK_STANDARD, "gfocce_c", bshape ); CHKFSTR ( CHK_STANDARD, "gfocce_c", abcorr ); CHKFSTR ( CHK_STANDARD, "gfocce_c", obsrvr ); /* Assign the SpiceBoolean report and interrupt flags. */ rep = rpt ; interrupt = bail; /* Store the input function pointers so these functions can be called by the GF adapters. */ zzadsave_c ( UDSTEP, (void *)(udstep) ); zzadsave_c ( UDREFN, (void *)(udrefn) ); zzadsave_c ( UDREPF, (void *)(udrepf) ); zzadsave_c ( UDREPI, (void *)(udrepi) ); zzadsave_c ( UDREPU, (void *)(udrepu) ); zzadsave_c ( UDBAIL, (void *)(udbail) ); /* If interrupt handling is enabled, and if the default bail-out routine gfbail_c is being used, set the SPICE interrupt handler. */ newHandler = SPICEFALSE; if ( bail ) { newHandler = ( (void *)udbail == (void *)gfbail_c ); if ( newHandler ) { defSigHandler = signal ( SIGINT, gfinth_c ); if ( defSigHandler == SIG_ERR ) { setmsg_c ( "Attempt to establish the CSPICE routine " "gfinth_c as the handler for the interrupt " "signal SIGINT failed." ); sigerr_c ( "SPICE(SIGNALFAILED)" ); chkout_c ( "gfocce_c" ); return; } } } /* Let the f2c'd routine do the work. We pass the adapter functions, not those provided as inputs, to the f2c'd routine. */ gfocce_ ( ( char * ) occtyp, ( char * ) front, ( char * ) fshape, ( char * ) fframe, ( char * ) back, ( char * ) bshape, ( char * ) bframe, ( char * ) abcorr, ( char * ) obsrvr, ( doublereal * ) &tol, ( U_fp ) zzadstep_c, ( U_fp ) zzadrefn_c, ( logical * ) &rep, ( S_fp ) zzadrepi_c, ( U_fp ) zzadrepu_c, ( S_fp ) zzadrepf_c, ( logical * ) &interrupt, ( L_fp ) zzadbail_c, ( doublereal * ) (cnfine->base), ( doublereal * ) (result->base), ( ftnlen ) strlen(occtyp), ( ftnlen ) strlen(front), ( ftnlen ) strlen(fshape), ( ftnlen ) strlen(fframe), ( ftnlen ) strlen(back), ( ftnlen ) strlen(bshape), ( ftnlen ) strlen(bframe), ( ftnlen ) strlen(abcorr), ( ftnlen ) strlen(obsrvr) ); /* If we've changed the signal handler, restore the previous one. */ if ( newHandler ) { sigPtr = signal ( SIGINT, defSigHandler ); if ( sigPtr == SIG_ERR ) { setmsg_c ( "Attempt to restore the previous handler " "for the interrupt signal SIGINT failed." ); sigerr_c ( "SPICE(SIGNALFAILED)" ); chkout_c ( "gfocce_c" ); return; } } /* Sync the output cell. */ if ( !failed_c() ) { zzsynccl_c ( F2C, result ) ; } chkout_c ( "gfocce_c" ); } /* End gfocce_c */