Index of Functions: A B C D E F G H I J K L M N O P Q R S T U V W X
Index Page gfsntc_c
Table of contents
Procedure Abstract Required_Reading Keywords Brief_I/O Detailed_Input | Detailed_Output Parameters Exceptions Files Particulars Examples | Restrictions Literature_References Author_and_Institution Version Index_Entries
#### Procedure
       gfsntc_c (GF, surface intercept vector coordinate search)

       void gfsntc_c ( ConstSpiceChar     * target,
                       ConstSpiceChar     * fixref,
                       ConstSpiceChar     * method,
                       ConstSpiceChar     * abcorr,
                       ConstSpiceChar     * obsrvr,
                       ConstSpiceChar     * dref,
                       ConstSpiceDouble     dvec   [3],
                       ConstSpiceChar     * crdsys,
                       ConstSpiceChar     * coord,
                       ConstSpiceChar     * relate,
                       SpiceDouble          refval,
                       SpiceDouble          adjust,
                       SpiceDouble          step,
                       SpiceInt             nintvls,
                       SpiceCell          * cnfine,
                       SpiceCell          * result  )
#### Abstract
       Determine time intervals for which a coordinate of an
       surface intercept position vector satisfies a numerical constraint.
#### Required_Reading
       GF
       SPK
       CK
       TIME
       WINDOWS
#### Keywords
       EVENT
       GEOMETRY
       SEARCH
       SEPARATION
#### Brief_I/O
       VARIABLE  I/O  DESCRIPTION
       --------  ---  --------------------------------------------------
       SPICE_GF_CNVTOL
                  P   Convergence tolerance.
       target     I   Name of the target body.
       fixref     I   Body fixed frame associated with `target'.
       method     I   Name of method type for surface intercept
                      calculation.
       abcorr     I   Aberration correction flag.
       obsrvr     I   Name of the observing body.
       dref       I   Reference frame of direction vector `dvec'.
       dvec       I   Pointing direction vector from `obsrvr'.
       crdsys     I   Name of the coordinate system containing `coord'.
       coord      I   Name of the coordinate of interest.
       relate     I   Relational operator.
       refval     I   Reference value.
       adjust     I   Adjustment value for absolute extrema searches.
       step       I   Step size used for locating extrema and roots.
       nintvls    I   Workspace window interval count.
       cnfine    I-O  SPICE window to which the search is confined.
       result     O   SPICE window containing results.
#### Detailed_Input
       target      is the string name of a target body. Optionally, you may
                   supply the integer ID code for the object as an
                   integer string. For example both "MOON" and "301"
                   are legitimate strings that indicate the moon is the
                   target body.

                   On calling gfsntc_c, the kernel pool must contain the radii
                   data corresponding to `target'.

       fixref      is the string name of the body-fixed, body-centered
                   reference frame associated with the target body `target'.

                   The SPICE frame subsystem must recognize the `fixref'
                   name.

       method      is the string name of the method to use for the surface
                   intercept calculation. The accepted values for `method':

                      "Ellipsoid"        The intercept computation uses
                                         a triaxial ellipsoid to model
                                         the surface of the target body.
                                         The ellipsoid's radii must be
                                         available in the kernel pool.

                   The `method' string lacks sensitivity to case, embedded,
                   leading and trailing blanks.

       abcorr      is the string description of the aberration corrections
                   to apply to the state evaluations to account for one-way
                   light time and stellar aberration.

                   Any aberration correction accepted by the SPICE
                   routine spkezr_c is accepted here. See the header
                   of spkezr_c for a detailed description of the
                   aberration correction options. For convenience,
                   the options are listed below:

                      "NONE"     Apply no correction. Returns the "true"
                                 geometric state.

                      "LT"       "Reception" case: correct for
                                 one-way light time using a Newtonian
                                 formulation.

                      "LT+S"     "Reception" case: correct for
                                 one-way light time and stellar
                                 aberration using a Newtonian
                                 formulation.

                      "CN"       "Reception" case: converged
                                 Newtonian light time correction.

                      "CN+S"     "Reception" case: converged
                                 Newtonian light time and stellar
                                 aberration corrections.

                      "XLT"      "Transmission" case: correct for
                                 one-way light time using a Newtonian
                                 formulation.

                      "XLT+S"    "Transmission" case: correct for
                                 one-way light time and stellar
                                 aberration using a Newtonian
                                 formulation.

                      "XCN"      "Transmission" case: converged
                                 Newtonian light time correction.

                      "XCN+S"    "Transmission" case: converged
                                 Newtonian light time and stellar
                                 aberration corrections.

                   The `abcorr' string lacks sensitivity to case, leading
                   and trailing blanks.

                   *Note*

                   When using a reference frame defined as a dynamic frame,
                   the user should realize defining an aberration correction
                   for the search different from that in the frames
                   definition will affect the search results.

                   In general, use the same aberration correction for
                   intercept point searches as used in the definition of a
                   dynamic frame (if applicable).

       obsrvr      is the string name of an observing body. Optionally, you
                   may supply the ID code of the object as an integer
                   string. For example, both "EARTH" and "399" are
                   legitimate strings to indicate the observer as Earth.

       dref        is the string name of the reference frame corresponding
                   to `dvec'.

                   The `dref' string lacks sensitivity to case, leading
                   and trailing blanks.

       dvec        is the pointing or boresight vector from the observer.
                   The intercept of this vector and `target' is the event of
                   interest.

       crdsys      is the string name of the coordinate system for which the
                   coordinate of interest is a member.

       coord       is the string name of the coordinate of interest in
                   `crdsys'.

                   The supported coordinate systems and coordinate names:

                      crdsys             coord               Range
                      ----------------   -----------------   ------------
                      "RECTANGULAR"      "X"
                                         "Y"
                                         "Z"

                      "LATITUDINAL"      "RADIUS"
                                         "LONGITUDE"         (-Pi,Pi]
                                         "LATITUDE"          [-Pi/2,Pi/2]

                      "RA/DEC"           "RANGE"
                                         "RIGHT ASCENSION"   [0,2Pi)
                                         "DECLINATION"       [-Pi/2,Pi/2]

                      "SPHERICAL"        "RADIUS"
                                         "COLATITUDE"        [0,Pi]
                                         "LONGITUDE"         (-Pi,Pi]

                      "CYLINDRICAL"      "RADIUS"
                                         "LONGITUDE"         [0,2Pi)
                                         "Z"

                      "GEODETIC"         "LONGITUDE"         (-Pi,Pi]
                                         "LATITUDE"          [-Pi/2,Pi/2]
                                         "ALTITUDE"

                      "PLANETOGRAPHIC"   "LONGITUDE"         [0,2Pi)
                                         "LATITUDE"          [-Pi/2,Pi/2]
                                         "ALTITUDE"

                   The "ALTITUDE" coordinates have a constant value of
                   zero +/- roundoff for ellipsoid targets.

                   Limit searches for coordinate events in the "GEODETIC"
                   and "PLANETOGRAPHIC" coordinate systems to `target' bodies
                   with axial symmetry in the equatorial plane, i.e.
                   equality of the body X and Y radii (oblate or prolate
                   spheroids).

                   Searches on "GEODETIC" or "PLANETOGRAPHIC" coordinates
                   requires body shape data, and in the case of
                   "PLANETOGRAPHIC" coordinates, body rotation data.

                   The body associated with "GEODETIC" or "PLANETOGRAPHIC"
                   coordinates is the center of the frame `fixref'.

       relate      is the string or character describing the relational
                   operator used to define a constraint on the selected
                   coordinate of the surface intercept vector. The result
                   window found by this routine indicates the time intervals
                   where the constraint is satisfied. Supported values of
                   `relate' and corresponding meanings are shown below:

                      ">"        The coordinate value is greater than the
                                 reference value `refval'.

                      "="        The coordinate value is equal to the
                                 reference value `refval'.

                      "<"        The coordinate value is less than the
                                 reference value `refval'.

                      "ABSMAX"   The coordinate value is at an absolute
                                 maximum.

                      "ABSMIN"   The coordinate value is at an absolute
                                 minimum.

                      "LOCMAX"   The coordinate value is at a local
                                 maximum.

                      "LOCMIN"   The coordinate value is at a local
                                 minimum.

                   The caller may indicate that the region of interest
                   is the set of time intervals where the quantity is
                   within a specified measure of an absolute extremum.
                   The argument `adjust' (described below) is used to
                   specify this measure.

                   Local extrema are considered to exist only in the
                   interiors of the intervals comprising the confinement
                   window:  a local extremum cannot exist at a boundary
                   point of the confinement window.

                   The `relate' string lacks sensitivity to case, leading
                   and trailing blanks.

       refval      is the double precision reference value used together
                   with the argument `relate' to define an equality or
                   inequality to satisfy by the selected coordinate of the
                   surface intercept vector. See the discussion of `relate'
                   above for further information.

                   The units of `refval' correspond to the type as defined
                   by `coord', radians for angular measures, kilometers for
                   distance measures.

       adjust      is a double precision value used to modify searches for
                   absolute extrema: when `relate' is set to "ABSMAX" or
                   "ABSMIN" and `adjust' is set to a positive value, gfsntc_c
                   finds times when the intercept vector coordinate is
                   within `adjust' radians/kilometers of the specified extreme
                   value.

                   For `relate' set to "ABSMAX", the `result' window contains
                   time intervals when the intercept vector coordinate has
                   values between absmax - adjust and `absmax'.

                   For `relate' set to "ABSMIN", the `result' window contains
                   time intervals when the intercept vector coordinate has
                   values between `absmin' and absmin + adjust.

                   `adjust' is not used for searches for local extrema,
                   equality or inequality conditions.

       step        is the double precision time step size to use in the
                   search.

                   Selection of the time step for surface intercept geometry
                   requires consideration of the mechanics of a surface
                   intercept event. In most cases, two distinct searches
                   will be needed, one to determine the windows when the
                   boresight vector intercepts the surface and then the
                   search based on the user defined constraints within those
                   windows. The boresight of nadir pointing instrument may
                   continually intercept a body, but an instrument scanning
                   across a disc will have configurations when the
                   boresight does not intercept the body.

                   The step size must be smaller than the shortest interval
                   within the confinement window over which the intercept
                   exists and also smaller than the shortest interval over
                   which the intercept does not exist.

                   For coordinates other than LONGITUDE and RIGHT ASCENSION,
                   the step size must be shorter than the shortest interval,
                   within the confinement window, over which the coordinate
                   is monotone increasing or decreasing.

                   For LONGITUDE and RIGHT ASCENSION, the step size must
                   be shorter than the shortest interval, within the
                   confinement window, over which either the sine or cosine
                   of the coordinate is monotone increasing or decreasing.

                   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.

       nintvls     is an integer parameter specifying the number of intervals
                   that can be accommodated by each of the dynamically allocated
                   workspace windows used internally by this routine.

                   In many cases, it's not necessary to compute an accurate
                   estimate of how many intervals are needed; rather, the user
                   can pick a size considerably larger than what's really
                   required.

                   However, since excessively large arrays can prevent
                   applications from compiling, linking, or running properly,
                   sometimes `nintvls' must be set according to the actual
                   workspace requirement. A rule of thumb for the number of
                   intervals needed is

                      nintvls  =  2*n  +  ( m / step )

                   where

                      n      is the number of intervals in the confinement
                             window.

                      m      is the measure of the confinement window, in units
                             of seconds.

                      step   is the search step size in seconds.

       cnfine      is a double precision 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.

                   In some cases the confinement window can be used to
                   greatly reduce the time period that must be searched
                   for the desired solution. See the -Particulars section
                   below for further discussion.

                   See the -Examples section below for a code example
                   that shows how to create a confinement window.

                   In some cases the observer's state may be computed at
                   times outside of `cnfine' by as much as 2 seconds. See
                   -Particulars for details.

                   `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 the SPICE window of intervals, contained within the
                   confinement window `cnfine', on which the specified
                   constraint is satisfied.

                   `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 gfsntc_c conducts its search.

                   The endpoints of the time intervals comprising `result' are
                   interpreted as seconds past J2000 TDB.

                   If the search is for local extrema, or for absolute
                   extrema with `adjust' set to zero, then normally each
                   interval of `result' will be a singleton: the left and
                   right endpoints of each interval will be identical.

                   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 also used for finding intermediate
                         results; in particular, SPICE_GF_CNVTOL is used for
                         finding the windows on which the specified coordinate
                         is increasing or decreasing. 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_NWMAX    is the number of workspace windows required by
                         this routine.

       See header file SpiceGF.h for declarations and descriptions of
       parameters used throughout the GF system.
#### 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. One technique to handle such a situation,
           slightly contract `result' using the window routine wncond_c.

       3)  If the number of intervals `nintvls' is less than 1, the error
           SPICE(VALUEOUTOFRANGE) is signaled.

       4)  If the window size of `result' is less than 2, the error
           SPICE(INVALIDDIMENSION) is signaled by a routine in the call
           tree of this routine.

       5)  If the output SPICE window `result' has insufficient capacity
           to contain the number of intervals on which the specified
           distance condition is met, an error is signaled
           by a routine in the call tree of this routine.

       6)  If an error (typically cell overflow) occurs during
           window arithmetic, the error is signaled by a routine
           in the call tree of this routine.

       7)  If the relational operator `relate' is not recognized, an
           error is signaled by a routine in the call tree of this
           routine.

       8)  If the aberration correction specifier contains an
           unrecognized value, an error is signaled by a routine in the
           call tree of this routine.

       9)  If `adjust' is negative, an error is signaled by a routine in
           the call tree of this routine.

       10) If either of the input body names do not map to NAIF ID
           codes, an error is signaled by a routine in the call tree of
           this routine.

       11) If required ephemerides or other kernel data are not
           available, an error is signaled by a routine in the call tree
           of this routine.

       12) If the search uses GEODETIC or PLANETOGRAPHIC coordinates, and
           the center body of the reference frame has unequal equatorial
           radii, an error is signaled by a routine in the call tree of
           this routine.

       13) If any of the `target', `fixref', `method', `abcorr',
           `abcorr', `dref', `crdsys', `coord' or `relate' input string
           pointers is null, the error SPICE(NULLPOINTER) is signaled.

       14) If any of the `target', `fixref', `method', `abcorr',
           `abcorr', `dref', `crdsys', `coord' or `relate' input strings
           has zero length, the error SPICE(EMPTYSTRING) is signaled.

       15) If any the `cnfine' or `result' cell arguments has a type
           other than SpiceDouble, the error SPICE(TYPEMISMATCH) is
           signaled.

       16) If memory cannot be allocated to create the temporary variable
           required for the execution of the underlying Fortran routine,
           the error SPICE(MALLOCFAILED) is signaled.
#### Files
       Appropriate SPK and PCK 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, observer, and any intermediate objects in
          a chain connecting the targets 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 using
          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 using furnsh_c.

       -  If non-inertial reference frames are used, then PCK
          files, frame kernels, C-kernels, and SCLK kernels may be
          needed.

       -  In some cases the observer's state may be computed at times
          outside of `cnfine' by as much as 2 seconds; data required to
          compute this state must be provided by loaded kernels. See
          -Particulars for details.

       Such kernel data are normally loaded once per program run, NOT
       every time this routine is called.
#### Particulars
       This routine provides a simpler, but less flexible interface
       than does the routine gfevnt_c for conducting searches for
       surface intercept vector coordinate value events.
       Applications that require support for progress reporting,
       interrupt handling, non-default step or refinement functions, or
       non-default convergence tolerance should call gfevnt_c rather than
       this routine.

       This routine determines a set of one or more time intervals
       within the confinement window when the selected coordinate of
       the surface intercept position vector satisfies a caller-specified
       constraint. 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
       ==================

       Regardless of the type of constraint selected by the caller, this
       routine starts the search for solutions by determining the time
       periods, within the confinement window, over which the specified
       coordinate function is monotone increasing and monotone
       decreasing. Each of these time periods is represented by a SPICE
       window. Having found these windows, all of the coordinate
       function's local extrema within the confinement window are known.
       Absolute extrema then can be found very easily.

       Within any interval of these "monotone" windows, there will be at
       most one solution of any equality constraint. Since the boundary
       of the solution set for any inequality constraint is contained in
       the union of

       -  the set of points where an equality constraint is met

       -  the boundary points of the confinement window

       the solutions of both equality and inequality constraints can be
       found easily once the monotone windows have been found.

       Step Size
       =========

       The monotone windows (described above) are found using a two-step
       search process. 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 sign of the rate of
       change of coordinate will be sampled. Starting at
       the left endpoint of an interval, samples will be taken at each
       step. If a change of sign is found, a root has been bracketed; at
       that point, the time at which the time derivative of the
       coordinate is zero can be found by a refinement process, for
       example, using a binary search.

       Note that the optimal choice of step size depends on the lengths
       of the intervals over which the coordinate function is monotone:
       the step size should be shorter than the shortest of these
       intervals (within the confinement window).

       The optimal step size is *not* necessarily related to the lengths
       of the intervals comprising the result window. For example, if
       the shortest monotone interval has length 10 days, and if the
       shortest result window interval has length 5 minutes, a step size
       of 9.9 days is still adequate to find all of the intervals in the
       result window. In situations like this, the technique of using
       monotone windows yields a dramatic efficiency improvement over a
       state-based search that simply tests at each step whether the
       specified constraint is satisfied. The latter type of search can
       miss solution intervals if the step size is longer than the
       shortest solution interval.

       Having some knowledge of the relative geometry of the target 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 default convergence tolerance
       used by this routine is set by the parameter SPICE_GF_CNVTOL (defined
       in 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.

       The user may change the convergence tolerance from the default
       SPICE_GF_CNVTOL value by calling the routine gfstol_c, e.g.

          gfstol_c ( tolerance value );

       Call gfstol_c prior to calling this routine. All subsequent
       searches will use the updated tolerance value.

       Setting 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. 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.

       Practical use of the coordinate search capability would likely
       consist of searches over multiple coordinate constraints to find
       time intervals that satisfies the constraints. An
       effective technique to accomplish such a search is
       to use the result window from one search as the confinement window
       of the next.

       Certain types of searches require the state of the observer,
       relative to the solar system barycenter, to be computed at times
       slightly outside the confinement window `cnfine'. The time window
       that is actually used is the result of "expanding" `cnfine' by a
       specified amount "T": each time interval of `cnfine' is expanded by
       shifting the interval's left endpoint to the left and the right
       endpoint to the right by T seconds. Any overlapping intervals are
       merged. (The input argument `cnfine' is not modified.)

       The window expansions listed below are additive: if both
       conditions apply, the window expansion amount is the sum of the
       individual amounts.

       -  If a search uses an equality constraint, the time window
          over which the state of the observer is computed is expanded
          by 1 second at both ends of all of the time intervals
          comprising the window over which the search is conducted.

       -  If a search uses stellar aberration corrections, the time
          window over which the state of the observer is computed is
          expanded as described above.

       When light time corrections are used, expansion of the search
       window also affects the set of times at which the light time-
       corrected state of the target is computed.

       In addition to the possible 2 second expansion of the search
       window that occurs when both an equality constraint and stellar
       aberration corrections are used, round-off error should be taken
       into account when the need for data availability is analyzed.

       Longitude and Right Ascension
       =============================

       The cyclic nature of the longitude and right ascension coordinates
       produces branch cuts at +/- 180 degrees longitude and 0-360
       longitude. Round-off error may cause solutions near these branches
       to cross the branch. Use of the SPICE routine wncond_c will contract
       solution windows by some epsilon, reducing the measure of the
       windows and eliminating the branch crossing. A one millisecond
       contraction will in most cases eliminate numerical round-off
       caused branch crossings.
#### 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 the time during 2007 for which the latitude of the
          intercept point of the vector pointing from the sun towards
          the earth in the IAU_EARTH frame equals zero i.e. the intercept
          point crosses the equator.

          Use the meta-kernel shown below to load the required SPICE
          kernels.

             KPL/MK

             File name: gfsntc_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
                ---------                     --------
                de414.bsp                     Planetary ephemeris
                pck00008.tpc                  Planet orientation and
                                              radii
                naif0008.tls                  Leapseconds

             \begindata

             KERNELS_TO_LOAD = ( 'naif0008.tls'
                                 'de414.bsp'
                                 'pck00008.tpc' )

             \begintext

             End of meta-kernel

          Use the kernel shown below to define a dynamic frame,
          Sun-Earth Motion.

             KPL/FK

             File name: gfsntc_sem.tf

             The Sun-Earth Motion frame is defined by the sun-to-earth
             direction vector as the X axis. The Y axis in the earth
             orbital plane, and Z completing the right hand system.

             \begindata

               FRAME_SEM                     =  10100000
               FRAME_10100000_NAME           = 'SEM'
               FRAME_10100000_CLASS          =  5
               FRAME_10100000_CLASS_ID       =  10100000
               FRAME_10100000_CENTER         =  10
               FRAME_10100000_RELATIVE       = 'J2000'
               FRAME_10100000_DEF_STYLE      = 'PARAMETERIZED'
               FRAME_10100000_FAMILY         = 'TWO-VECTOR'
               FRAME_10100000_PRI_AXIS       = 'X'
               FRAME_10100000_PRI_VECTOR_DEF = 'OBSERVER_TARGET_POSITION'
               FRAME_10100000_PRI_OBSERVER   = 'SUN'
               FRAME_10100000_PRI_TARGET     = 'EARTH'
               FRAME_10100000_PRI_ABCORR     = 'NONE'
               FRAME_10100000_SEC_AXIS       = 'Y'
               FRAME_10100000_SEC_VECTOR_DEF = 'OBSERVER_TARGET_VELOCITY'
               FRAME_10100000_SEC_OBSERVER   = 'SUN'
               FRAME_10100000_SEC_TARGET     = 'EARTH'
               FRAME_10100000_SEC_ABCORR     = 'NONE'
               FRAME_10100000_SEC_FRAME      = 'J2000'

             \begintext

             End of frames kernel

          Example code begins here.

          /.
             Program gfsntc_ex1
          ./

          #include <stdio.h>
          #include <stdlib.h>
          #include <string.h>

          #include "SpiceUsr.h"

          #define   MAXWIN   1000
          #define   TIMFMT   "YYYY-MON-DD HR:MN:SC.###### (TDB) ::TDB ::RND"
          #define   TIMLEN   64

          int main( )
          {

             /.
             Create the needed windows. Note, one window
             consists of two values, so the total number
             of cell values to allocate is twice
             the number of intervals.
             ./
             SPICEDOUBLE_CELL ( result, 2*MAXWIN );
             SPICEDOUBLE_CELL ( cnfine, 2       );

             SpiceDouble       begtim;
             SpiceDouble       endtim;
             SpiceDouble       step;
             SpiceDouble       adjust;
             SpiceDouble       refval;
             SpiceDouble       strpnt;
             SpiceDouble       endpnt;

             SpiceChar         begstr [ TIMLEN ];
             SpiceChar         endstr [ TIMLEN ];
             SpiceChar       * relate = "=";
             SpiceChar       * crdsys = "LATITUDINAL";
             SpiceChar       * coord  = "LATITUDE";
             SpiceChar       * method = "Ellipsoid";
             SpiceChar       * targ   = "EARTH";
             SpiceChar       * obsrvr = "SUN";
             SpiceChar       * dref   = "SEM";
             SpiceDouble       dvec[] = { 1, 0, 0 };
             SpiceChar       * fixref = "IAU_EARTH";
             SpiceChar       * abcorr = "NONE";

             SpiceInt          count;
             SpiceInt          i;

             /.
             Search for a condition where the latitudinal system coordinate
             latitude in the IAU_EARTH frame has value zero. In this case,
             the pointing vector, 'DVEC', defines the vector direction
             pointing at the earth from the sun.
             ./

             /.
             Load kernels.
             ./
             furnsh_c( "gfsntc_ex1.tm" );
             furnsh_c( "gfsntc_sem.tf" );

             /.
             Store the time bounds of our search interval in
             the cnfine confinement window.
             ./
             str2et_c( "2007 JAN 01", &begtim );
             str2et_c( "2008 JAN 01", &endtim );

             wninsd_c ( begtim, endtim, &cnfine );

             /.
             The latitude varies relatively slowly, ~46 degrees during the
             year. The extrema occur approximately every six months.
             Search using a step size less than half that value (180 days).
             For this example use ninety days (in units of seconds).
             ./
             step   = (90.)*spd_c();
             adjust = 0.;
             refval = 0;

             /.
             List the beginning and ending points in each interval
             if result contains data.
             ./
             gfsntc_c ( targ,
                        fixref,
                        method,
                        abcorr,
                        obsrvr,
                        dref,
                        dvec,
                        crdsys,
                        coord,
                        relate,
                        refval,
                        adjust,
                        step,
                        MAXWIN,
                        &cnfine,
                        &result  );

             count = wncard_c( &result );

             /.
             Display the results.
             ./
             if (count == 0 )
             {
                printf ( "Result window is empty.\n\n" );
             }
             else
             {
                for ( i = 0;  i < count;  i++ )
                {

                   /.
                   Fetch the endpoints of the Ith interval
                   of the result window.
                   ./
                   wnfetd_c ( &result, i, &strpnt, &endpnt );

                   if ( strpnt == endpnt )
                   {
                      timout_c ( strpnt, TIMFMT, TIMLEN, begstr );
                      printf ( "Event time: %s\n", begstr );
                   }
                   else
                   {

                      timout_c ( strpnt, TIMFMT, TIMLEN, begstr );
                      timout_c ( endpnt, TIMFMT, TIMLEN, endstr );

                      printf ( "Interval %d\n", i + 1);
                      printf ( "From : %s \n", begstr );
                      printf ( "To   : %s \n", endstr );
                      printf( " \n" );
                   }

                }
             }

             kclear_c();
             return( 0 );
          }

          When this program was executed on a Mac/Intel/cc/64-bit
          platform, the output was:

          Event time: 2007-MAR-21 00:01:25.495120 (TDB)
          Event time: 2007-SEP-23 09:46:39.574124 (TDB)

       2) Find the time during 2007 for which the intercept point on the
          earth of the sun-to-earth vector as described in Example 1 in
          the IAU_EARTH frame lies within a geodetic latitude-longitude
          "box" defined as

              16 degrees <= latitude  <= 17 degrees
              85 degrees <= longitude <= 86 degrees

          This problem requires four searches, each search on one of the
          box restrictions. The user needs also realize the temporal
          behavior of latitude greatly differs from that of the
          longitude. The intercept latitude varies between approximately
          23.44 degrees and -23.44 degrees during the year. The intercept
          longitude varies between -180 degrees and 180 degrees in one
          day.

          Use the meta-kernel and the frames kernel from the first
          example.

          Example code begins here.

          /.
             Program gfsntc_ex2
          ./

          #include <stdio.h>
          #include <stdlib.h>
          #include <string.h>

          #include "SpiceUsr.h"

          #define   MAXWIN   100
          #define   TIMFMT   "YYYY-MON-DD HR:MN:SC.###### (TDB) ::TDB ::RND"
          #define   STRLEN   64

          int main( int argc, char **argv )
          {

             /.
             Create the needed windows. Note, one window
             consists of two values, so the total number
             of cell values to allocate equals twice
             the number of intervals.
             ./
             SPICEDOUBLE_CELL ( result1, 2*MAXWIN );
             SPICEDOUBLE_CELL ( result2, 2*MAXWIN );
             SPICEDOUBLE_CELL ( result3, 2*MAXWIN );
             SPICEDOUBLE_CELL ( result4, 2*MAXWIN );
             SPICEDOUBLE_CELL ( cnfine, 2       );

             SpiceDouble       begtim;
             SpiceDouble       endtim;
             SpiceDouble       step;
             SpiceDouble       adjust;
             SpiceDouble       refval;
             SpiceDouble       strpnt;
             SpiceDouble       endpnt;

             SpiceChar         begstr [ STRLEN ];
             SpiceChar         endstr [ STRLEN ];
             SpiceChar       * target = "EARTH";
             SpiceChar       * obsrvr = "SUN";
             SpiceChar       * dref   = "SEM";
             SpiceDouble       dvec[] = { 1, 0, 0 };
             SpiceChar       * fixref = "IAU_EARTH";
             SpiceChar       * method = "Ellipsoid";
             SpiceChar       * crdsys = "GEODETIC";

             /.
             Use the same aberration correction flag as that in the SEM frame
             definition.
             ./
             SpiceChar       * abcorr = "NONE";

             SpiceInt          count;
             SpiceInt          i;

             /.
             Load kernels.
             ./
             furnsh_c( "gfsntc_ex1.tm" );
             furnsh_c( "gfsntc_sem.tf" );

             /.
             Store the time bounds of our search interval in
             the cnfine confinement window.
             ./
             str2et_c( "2007 JAN 01", &begtim );
             str2et_c( "2008 JAN 01", &endtim );

             wninsd_c ( begtim, endtim, &cnfine );

             /.
             Perform four searches to determine the times when the
             latitude-longitude box restriction conditions apply. In this case,
             the pointing  vector, 'dvec', defines the vector direction
             pointing at the earth from the sun.

             Perform the searches such that the result window of a search
             serves as the confinement window of the subsequent search.

             Since the latitude coordinate varies slowly and is well behaved
             over the time of the confinement window, search first for the
             windows satisfying the latitude requirements, then use that result
             as confinement for the longitude search.
             ./

             /.
             The latitude varies relatively slowly, ~46 degrees during the
             year. The extrema occur approximately every six months.
             Search using a step size less than half that value (180 days).
             For this example use ninety days (in units of seconds).
             ./

             step   = (90.)*spd_c();
             adjust = 0.;

             {
             SpiceChar       * coord  = "LATITUDE";
             SpiceChar       * relate = ">";

             refval = 16. *rpd_c();

             gfsntc_c (  target,  fixref,
                         method,  abcorr, obsrvr,
                         dref,    dvec,
                         crdsys,  coord,
                         relate,  refval,
                         adjust,  step,
                         MAXWIN,
                         &cnfine, &result1 );
             }

             {
             SpiceChar       * coord  = "LATITUDE";
             SpiceChar       * relate = "<";

             refval = 17. *rpd_c();

             gfsntc_c (  target,  fixref,
                         method,  abcorr, obsrvr,
                         dref,    dvec,
                         crdsys,  coord,
                         relate,  refval,
                         adjust,  step,
                         MAXWIN,
                         &result1, &result2 );
             }

             /.
             Now the longitude search.
             ./

             /.
             Reset the step size to something appropriate for the 360
             degrees in 24 hours domain. The longitude shows near
             linear behavior so use a step size less than half the period
             of twelve hours. Ten hours will suffice in this case.
             ./
             step   = (10./24.)*spd_c();

             {
             SpiceChar       * coord  = "LONGITUDE";
             SpiceChar       * relate = ">";

             refval = 85. *rpd_c();

             gfsntc_c (  target,  fixref,
                         method,  abcorr, obsrvr,
                         dref,    dvec,
                         crdsys,  coord,
                         relate,  refval,
                         adjust,  step,
                         MAXWIN,
                         &result2, &result3 );

             /.
             Contract the endpoints of each window to account
             for possible round-off error at the -180/180 degree branch.

             A contraction value of a millisecond should eliminate
             any round-off caused branch crossing.
             ./

             wncond_c( 1e-3, 1e-3, &result3 );
             }

             {
             SpiceChar       * coord  = "LONGITUDE";
             SpiceChar       * relate = "<";

             refval = 86. *rpd_c();

             gfsntc_c (  target,  fixref,
                         method,  abcorr, obsrvr,
                         dref,    dvec,
                         crdsys,  coord,
                         relate,  refval,
                         adjust,  step,
                         MAXWIN,
                         &result3, &result4 );
             }

             /.
             List the beginning and ending points in each interval
             if result contains data.
             ./
             count = wncard_c( &result4 );

             /.
             Display the results.
             ./
             if (count == 0 )
             {
                printf ( "Result window is empty.\n\n" );
             }
             else
             {
                for ( i = 0;  i < count;  i++ )
                {

                   /.
                   Fetch the endpoints of the Ith interval
                   of the result window.
                   ./
                   wnfetd_c ( &result4, i, &strpnt, &endpnt );

                   timout_c ( strpnt, TIMFMT, STRLEN, begstr );
                   timout_c ( endpnt, TIMFMT, STRLEN, endstr );

                   printf ( "Interval %d\n", i + 1);
                   printf ( "Beginning TDB %s \n",   begstr );
                   printf ( "Ending TDB    %s \n\n", endstr );

                }
             }

             kclear_c();
             return( 0 );
          }

          When this program was executed on a Mac/Intel/cc/64-bit
          platform, the output was:

          Interval 1
          Beginning TDB 2007-MAY-05 06:14:04.637735 (TDB)
          Ending TDB    2007-MAY-05 06:18:03.621906 (TDB)

          Interval 2
          Beginning TDB 2007-MAY-06 06:13:59.583483 (TDB)
          Ending TDB    2007-MAY-06 06:17:58.569239 (TDB)

          Interval 3
          Beginning TDB 2007-MAY-07 06:13:55.102940 (TDB)
          Ending TDB    2007-MAY-07 06:17:54.090298 (TDB)

          Interval 4
          Beginning TDB 2007-AUG-06 06:23:17.282927 (TDB)
          Ending TDB    2007-AUG-06 06:27:16.264009 (TDB)

          Interval 5
          Beginning TDB 2007-AUG-07 06:23:10.545441 (TDB)
          Ending TDB    2007-AUG-07 06:27:09.524924 (TDB)

          Interval 6
          Beginning TDB 2007-AUG-08 06:23:03.233996 (TDB)
          Ending TDB    2007-AUG-08 06:27:02.211888 (TDB)

          Interval 7
          Beginning TDB 2007-AUG-09 06:22:55.351256 (TDB)
          Ending TDB    2007-AUG-09 06:26:54.327565 (TDB)
#### Restrictions
       1)  The kernel files to be used by this routine must be loaded
           (normally using the CSPICE routine furnsh_c) before this
           routine is called.

       2)  This routine has the side effect of re-initializing the
           coordinate quantity utility package. Callers may
           need to re-initialize the package after calling this routine.
#### Literature_References
       None.
#### Author_and_Institution
       N.J. Bachman        (JPL)
       J. Diaz del Rio     (ODC Space)
       E.D. Wright         (JPL)
#### Version
       -CSPICE Version 1.1.0, 01-NOV-2021 (JDR) (EDW)

           Added use of ALLOC_CHECK_INTRA to check net null effect on
           alloc count.

           Updated header to describe use of expanded confinement window.

           Edited the header to comply with NAIF standard. Renamed
           example's meta-kernel. Changed variable names "beg" and "end" to
           "strpnt" and "endpnt" in code examples.

           Added entries #3, #4 and #15 in -Exceptions section.

           Updated the description of "nintvls", "cnfine" and "result" arguments.

       -CSPICE Version 1.0.2, 31-JUL-2014 (EDW)

           Edit to header, replaced ' character with character " to indicate
           C strings.

       -CSPICE Version 1.0.1, 28-FEB-2013 (NJB) (EDW)

           Header was updated to discuss use of gfstol_c.

           Edit to comments to correct search description.

           Edits to and corrections of argument descriptions and
           header.

       -CSPICE Version 1.0.0, 17-FEB-2009 (EDW)
#### Index_Entries
       GF surface intercept coordinate search
#### Link to routine gfsntc_c source file gfsntc_c.c

    Fri Dec 31 18:41:07 2021