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Index Page getfov_c

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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

       getfov_c ( Get instrument FOV parameters )

       void getfov_c ( SpiceInt        instid,
                       SpiceInt        room,
                       SpiceInt        shapelen,
                       SpiceInt        framelen,
                       SpiceChar     * shape,
                       SpiceChar     * frame,
                       SpiceDouble     bsight [3],
                       SpiceInt      * n,
                       SpiceDouble     bounds [][3] )

#### Abstract

       Return the field-of-view (FOV) parameters for a specified
       instrument. The instrument is specified by its NAIF ID code.

#### Required_Reading

       NAIF_IDS

#### Keywords

       FOV
       INSTRUMENT

#### Brief_I/O

       VARIABLE  I/O  DESCRIPTION
       --------  ---  --------------------------------------------------
       instid     I   NAIF ID of an instrument.
       room       I   Maximum number of vectors that can be returned.
       shapelen   I   Space available in the string `shape'.
       framelen   I   Space available in the string `frame'.
       shape      O   Instrument FOV shape.
       frame      O   Name of the frame in which FOV vectors are defined.
       bsight     O   Boresight vector.
       n          O   Number of boundary vectors returned.
       bounds     O   FOV boundary vectors.

#### Detailed_Input

       instid      is the NAIF ID of an instrument.

       room        is the maximum number of 3-dimensional vectors that can
                   be returned in `bounds'.

       shapelen    is the maximum allowed length of the output string
                   `shape'. This length must be large enough to hold the
                   output string plus the null-terminator character. If the
                   output string is expected to have X characters, `shapelen'
                   should be at least X+1.

       framelen    is the maximum allowed length of the output string
                   `frame'. This length must be large enough to hold the
                   output string plus the null-terminator character. If the
                   output string is expected to have X characters, `framelen'
                   should be at least X+1.

#### Detailed_Output

       shape       is a character string that describes the "shape" of
                   the field of view. Possible values returned are:

                      "POLYGON"
                      "RECTANGLE"
                      "CIRCLE"
                      "ELLIPSE"

                   If the value of `shape' is "POLYGON" the field of view
                   of the instrument is a pyramidal polyhedron. The
                   vertex of the pyramid is at the instrument focal
                   point. The rays along the edges of the pyramid are
                   parallel to the vectors returned in `bounds'.

                   If the value of `shape' is "RECTANGLE" the field of view
                   of the instrument is a rectangular pyramid. The vertex
                   of the pyramid is at the instrument focal point. The
                   rays along the edges of the pyramid are parallel to
                   the vectors returned in `bounds'. Moreover, in this
                   case, the boresight points along the axis of symmetry
                   of the rectangular pyramid.

                   If the value of `shape' is "CIRCLE" the field of view of
                   the instrument is a circular cone centered on the
                   boresight vector. The vertex of the cone is at the
                   instrument focal point. A single vector will be
                   returned in `bounds'. This vector will be parallel to a
                   ray that lies in the cone that makes up the boundary
                   of the field of view.

                   If the value of `shape' is "ELLIPSE" the field of view
                   of the instrument is an elliptical cone with the
                   boresight vector as the axis of the cone. In this
                   case two vectors are returned in `bounds'. One of the
                   vectors returned in `bounds' points to the end of the
                   semi-major axis of a perpendicular cross section of
                   the elliptic cone. The other vector points to the end
                   of the semi-minor axis of a perpendicular cross
                   section of the cone.

       frame       is the name of the reference frame in which the field
                   of view boundary vectors are defined.

       bsight      is a vector representing the principal instrument view
                   direction that can be

                      -  the central pixel view direction,
                      -  the optical axis direction,
                      -  the FOV geometric center view direction,
                      -  an axis of the FOV frame,

                   or any other vector specified for this purpose
                   in the IK FOV definition. The length of `bsight'
                   is not specified other than being non-zero.

       n           is the number of boundary vectors returned.

       bounds      is an array of vectors that point to the "corners" of
                   the instrument field of view. (See the discussion
                   accompanying `shape' for an expansion of the term
                   "corner of the field of view.") Note that the vectors
                   returned in `bounds' are not necessarily unit vectors.
                   Their magnitudes will be as set in the IK (for
                   'CORNERS'-style FOV specifications) or the same as the
                   magnitude of the boresight (for 'ANGLES'-style FOV
                   specifications.)

#### Parameters

       MINCOS      This parameter is the lower limit on the value of the
                   cosine of the cross or reference angles in the 'ANGLES'
                   specification cases (see -Particulars for further
                   discussion). The parameter and its current value,
                   1.0x10^(-15), are employed in the C code derived from the
                   Fortran version of GETFOV that this wrapper invokes.

#### Exceptions

       1)  If the frame associated with the instrument can not be found,
           the error SPICE(FRAMEMISSING) is signaled by a routine in the
           call tree of this routine.

       2)  If the shape of the instrument field of view can not be found
           in the kernel pool, the error SPICE(SHAPEMISSING) is signaled
           by a routine in the call tree of this routine signaled.

       3)  If the FOV_SHAPE specified by the instrument kernel is not one
           of the four values: 'CIRCLE', 'POLYGON', 'ELLIPSE', or
           'RECTANGLE', the error SPICE(SHAPENOTSUPPORTED) is signaled by
           a routine in the call tree of this routine. If the 'ANGLES'
           specification is used, FOV_SHAPE must be one of the three
           values: 'CIRCLE', 'ELLIPSE', or 'RECTANGLE'.

       4)  If the direction of the boresight cannot be located in the
           kernel pool, the error SPICE(BORESIGHTMISSING) is signaled by
           a routine in the call tree of this routine.

       5)  If the number of components for the boresight vector in the
           kernel pool is not 3, or they are not numeric, the error
           SPICE(BADBORESIGHTSPEC) is signaled by a routine in the call
           tree of this routine.

       6)  If the boresight vector is the zero vector, the error
           SPICE(ZEROBORESIGHT) is signaled by a routine in the call
           tree of this routine.

       7)  If the 'ANGLES' specification is not present in the kernel
           pool and the boundary vectors for the edge of the field of
           view cannot be found in the kernel pool, the error
           SPICE(BOUNDARYMISSING) is signaled by a routine in the call
           tree of this routine.

       8)  If there is insufficient room (as specified by the argument
           `room') to return all of the vectors associated with the
           boundary of the field of view, the error SPICE(BOUNDARYTOOBIG)
           is signaled by a routine in the call tree of this routine.

       9)  If the number of components of vectors making up the field of
           view is not a multiple of 3, the error SPICE(BADBOUNDARY) is
           signaled by a routine in the call tree of this routine.

       10) If the number of components of vectors making up the field of
           view is not compatible with the shape specified for the field
           of view, the error SPICE(BADBOUNDARY) is signaled by a routine
           in the call tree of this routine.

       11) If the reference vector for the 'ANGLES' specification can not
           be found in the kernel pool, the error SPICE(REFVECTORMISSING)
           is signaled by a routine in the call tree of this routine.

       12) If the reference vector stored in the kernel pool to support
           the 'ANGLES' specification contains an incorrect number of
           components, contains 3 character components, or is parallel to
           the boresight, the error SPICE(BADREFVECTORSPEC) is signaled
           by a routine in the call tree of this routine.

       13) If the 'ANGLES' specification is present in the kernel pool
           and the reference angle stored in the kernel pool to support
           the 'ANGLES' specification is absent from the kernel pool, the
           error SPICE(REFANGLEMISSING) is signaled by a routine in the
           call tree of this routine.

       14) If the keyword that stores the angular units for the angles
           used in the 'ANGLES' specification is absent from the kernel
           pool, the error SPICE(UNITSMISSING) is signaled by a routine
           in the call tree of this routine.

       15) If the value used for the units in the 'ANGLES' specification
           is not one of the supported angular units of convrt_c, an error
           is signaled by a routine in the call tree of this routine.

       16) If the keyword that stores the cross angle for the 'ANGLES'
           specification is needed and is absent from the kernel pool,
           the error SPICE(CROSSANGLEMISSING) is signaled by a routine in
           the call tree of this routine.

       17) If the angles for the 'RECTANGLE'/'ANGLES' specification case
           have cosines that are less than those stored in the parameter
           MINCOS, the error SPICE(BADBOUNDARY) is signaled by a routine
           in the call tree of this routine.

       18) If the class specification contains something other than
           'ANGLES' or 'CORNERS', the error SPICE(UNSUPPORTEDSPEC) is
           signaled by a routine in the call tree of this routine.

       19) In the event that the CLASS_SPEC keyword is absent from the
           kernel pool for the instrument whose FOV is sought, this
           module assumes the 'CORNERS' specification is to be utilized.

       20) If any of the `shape' or `frame' output string pointers is
           null, the error SPICE(NULLPOINTER) is signaled.

       21) If any of the `shape' or `frame' output strings has length
           less than two characters, the error SPICE(STRINGTOOSHORT) is
           signaled, since the output string is too short to contain one
           character of output data plus a null terminator.

#### Files

       This routine relies upon having successfully loaded an instrument
       kernel (IK file) via the routine furnsh_c prior to calling this
       routine.

#### Particulars

       This routine provides a common interface for retrieving from the
       kernel pool the geometric characteristics of an instrument field
       of view for a wide variety of remote sensing instruments
       across many different space missions.

       Given the NAIF instrument ID, (and having "loaded" the
       instrument field of view description via the routine furnsh_c)
       this routine returns the boresight of the instrument, the
       "shape" of the field of view, a collection of vectors
       that point along the edges of the field of view, and the
       name of the reference frame in which these vectors are defined.

       Currently this routine supports two classes of specifications
       for FOV definitions: "corners" and "angles".

       The "corners" specification requires that the following keywords
       defining the shape, boresight, boundary vectors, and reference
       frame of the FOV be provided in one of the text kernel files
       (normally an IK file) loaded into the kernel pool (in the
       keywords below <INSTID> is replaced with the instrument ID as
       passed into the module):

          INS<INSTID>_FOV_CLASS_SPEC         must be set to 'CORNERS' or
                                             omitted to indicate the
                                             "corners"-class
                                             specification.

          INS<INSTID>_FOV_SHAPE              must be set to one of these
                                             values:

                                                'CIRCLE'
                                                'ELLIPSE'
                                                'RECTANGLE'
                                                'POLYGON'

          INS<INSTID>_FOV_FRAME              must contain the name of
                                             the frame in which the
                                             boresight and boundary
                                             corner vectors are defined.

          INS<INSTID>_BORESIGHT              must be set to a 3D vector
                                             defining the boresight in
                                             the FOV frame specified in
                                             the FOV_FRAME keyword.

          INS<INSTID>_FOV_BOUNDARY   or
          INS<INSTID>_FOV_BOUNDARY_CORNERS   must be set to one (for
                                             FOV_SHAPE = 'CIRCLE'), two
                                             (for FOV_SHAPE =
                                             'ELLIPSE'), four (for
                                             FOV_SHAPE = 'RECTANGLE'),
                                             or three or more (for
                                             'POLYGON') 3D vectors
                                             defining the corners of the
                                             FOV in the FOV frame
                                             specified in the FOV_FRAME
                                             keyword. The vectors should
                                             be listed in either
                                             clockwise or
                                             counterclockwise order.
                                             This is required by some
                                             SPICE routines that make
                                             use of FOV specifications.

       The "angles" specification requires the following keywords
       defining the shape, boresight, reference vector, reference and
       cross angular extents of the FOV be provided in one of the text
       kernel files (normally an IK file) loaded into the kernel
       pool (in the keywords below <INSTID> is replaced with the
       instrument ID as passed into the module):

          INS<INSTID>_FOV_CLASS_SPEC         must be set to 'ANGLES' to
                                             indicate the "angles"-class
                                             specification.

          INS<INSTID>_FOV_SHAPE              must be set to one of these
                                             values:

                                                'CIRCLE'
                                                'ELLIPSE'
                                                'RECTANGLE'

          INS<INSTID>_FOV_FRAME              must contain the name of
                                             the frame in which the
                                             boresight and the computed
                                             boundary corner vectors are
                                             defined.

          INS<INSTID>_BORESIGHT              must be set to a 3D vector
                                             defining the boresight in
                                             the FOV frame specified in
                                             the FOV_FRAME keyword.

          INS<INSTID>_FOV_REF_VECTOR         must be set to a 3D vector
                                             that together with the
                                             boresight vector defines
                                             the plane in which the
                                             first angular extent of the
                                             FOV specified in the
                                             FOV_REF_ANGLE keyword is
                                             measured.

          INS<INSTID>_FOV_REF_ANGLE          must be set to the angle
                                             that is 1/2 of the total
                                             FOV angular extent in the
                                             plane defined by the
                                             boresight and the vector
                                             specified in the
                                             FOV_REF_VECTOR keyword. The
                                             the FOV angular half-extents
                                             are measured from the
                                             boresight vector.

          INS<INSTID>_FOV_CROSS_ANGLE        must be set to the angle
                                             that is 1/2 of the total
                                             FOV angular extent in the
                                             plane containing the
                                             boresight and perpendicular
                                             to the plane defined by the
                                             boresight and the vector
                                             specified in the
                                             FOV_REF_VECTOR keyword. The
                                             the FOV angular half-extents
                                             are measured from the
                                             boresight vector. This
                                             keyword is not required for
                                             FOV_SHAPE = 'CIRCLE'.

          INS<INSTID>_FOV_ANGLE_UNITS        must specify units for the
                                             angles given in the
                                             FOV_REF_ANGLE and
                                             FOV_CROSS_ANGLE keywords.
                                             Any angular units
                                             recognized by convrt_c are
                                             acceptable.

       The INS<INSTID>_FOV_REF_ANGLE and INS<INSTID>_FOV_CROSS_ANGLE
       keywords can have any values for the 'CIRCLE' and 'ELLIPSE'
       FOV shapes but must satisfy the condition cos( angle ) > 0 for
       the 'RECTANGLE' shape.

       This routine is intended to be an intermediate level routine.
       It is expected that users of this routine will be familiar
       with the SPICE frames subsystem and will be comfortable writing
       software to further manipulate the vectors retrieved by this
       routine.

#### Examples

       The numerical results shown for this example 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) Load an IK, fetch the parameters for each of the FOVs defined
          within and print these parameters to the screen.

          Use the kernel shown below, an IK defining four FOVs of
          various shapes and sizes, to load the FOV definitions.

             KPL/IK

             File name: getfov_ex1.ti

             The keywords below define a circular, 10-degree wide FOV with
             the boresight along the +Z axis of the 'SC999_INST001' frame
             for an instrument with ID -999001 using the "angles"-class
             specification.

             \begindata
                INS-999001_FOV_CLASS_SPEC       = 'ANGLES'
                INS-999001_FOV_SHAPE            = 'CIRCLE'
                INS-999001_FOV_FRAME            = 'SC999_INST001'
                INS-999001_BORESIGHT            = ( 0.0, 0.0, 1.0 )
                INS-999001_FOV_REF_VECTOR       = ( 1.0, 0.0, 0.0 )
                INS-999001_FOV_REF_ANGLE        = ( 5.0 )
                INS-999001_FOV_ANGLE_UNITS      = ( 'DEGREES' )
             \begintext

             The keywords below define an elliptical FOV with 2- and
             4-degree angular extents in the XZ and XY planes and the
             boresight along the +X axis of the 'SC999_INST002' frame for
             an instrument with ID -999002 using the "corners"-class
             specification.

             \begindata
                INS-999002_FOV_SHAPE            = 'ELLIPSE'
                INS-999002_FOV_FRAME            = 'SC999_INST002'
                INS-999002_BORESIGHT            = ( 1.0, 0.0, 0.0 )
                INS-999002_FOV_BOUNDARY_CORNERS = ( 1.0, 0.0, 0.01745506,
                                                 1.0, 0.03492077, 0.0 )
             \begintext

             The keywords below define a rectangular FOV with 1.2- and
             0.2-degree angular extents in the ZX and ZY planes and the
             boresight along the +Z axis of the 'SC999_INST003' frame for
             an instrument with ID -999003 using the "angles"-class
             specification.

             \begindata
                INS-999003_FOV_CLASS_SPEC       = 'ANGLES'
                INS-999003_FOV_SHAPE            = 'RECTANGLE'
                INS-999003_FOV_FRAME            = 'SC999_INST003'
                INS-999003_BORESIGHT            = ( 0.0, 0.0, 1.0 )
                INS-999003_FOV_REF_VECTOR       = ( 1.0, 0.0, 0.0 )
                INS-999003_FOV_REF_ANGLE        = ( 0.6 )
                INS-999003_FOV_CROSS_ANGLE      = ( 0.1 )
                INS-999003_FOV_ANGLE_UNITS      = ( 'DEGREES' )
             \begintext

             The keywords below define a triangular FOV with the boresight
             along the +Y axis of the 'SC999_INST004' frame for an
             instrument with ID -999004 using the "corners"-class
             specification.

             \begindata
                INS-999004_FOV_SHAPE            = 'POLYGON'
                INS-999004_FOV_FRAME            = 'SC999_INST004'
                INS-999004_BORESIGHT            = (  0.0,  1.0,  0.0 )
                INS-999004_FOV_BOUNDARY_CORNERS = (  0.0,  0.8,  0.5,
                                                     0.4,  0.8, -0.2,
                                                    -0.4,  0.8, -0.2 )
             \begintext

             End of IK

          Example code begins here.

          /.
             Program getfov_ex1
          ./
          #include <stdio.h>
          #include "SpiceUsr.h"

          #define      MAXBND            4
          #define      NUMINS            4
          #define      WDSIZE            32

          int main (void)
          {

             SpiceChar    frame  [WDSIZE];
             SpiceChar    shape  [WDSIZE];

             SpiceDouble  bounds [MAXBND][3];
             SpiceDouble  bsight [3];

             SpiceInt     i;
             SpiceInt     insids [NUMINS] =
                              { -999001, -999002, -999003, -999004};
             SpiceInt     j;
             SpiceInt     n;

             furnsh_c( "getfov_ex1.ti" );

             printf( "--------------------------------------\n" );
             for ( i = 0; i < NUMINS; i++ ) {

                getfov_c ( insids[i], MAXBND, WDSIZE, WDSIZE,
                           shape, frame, bsight, &n, bounds );

                printf( "Instrument ID: %d\n", insids[i] );
                printf( "    FOV shape: %s\n",  shape     );
                printf( "    FOV frame: %s\n",  frame     );
                printf( "FOV boresight: %9.6f %9.6f %9.6f\n",
                          bsight[0], bsight[1], bsight[2] );
                printf( "  FOV corners: \n" );
                for ( j = 0; j < n; j++ ) {
                   printf( "               %9.6f %9.6f %9.6f\n",
                           bounds[j][0], bounds[j][1], bounds[j][2] );
                }
                printf( "--------------------------------------\n" );
             }
             return(0);
          }

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

          --------------------------------------
          Instrument ID: -999001
              FOV shape: CIRCLE
              FOV frame: SC999_INST001
          FOV boresight:  0.000000  0.000000  1.000000
            FOV corners:
                          0.087156  0.000000  0.996195
          --------------------------------------
          Instrument ID: -999002
              FOV shape: ELLIPSE
              FOV frame: SC999_INST002
          FOV boresight:  1.000000  0.000000  0.000000
            FOV corners:
                          1.000000  0.000000  0.017455
                          1.000000  0.034921  0.000000
          --------------------------------------
          Instrument ID: -999003
              FOV shape: RECTANGLE
              FOV frame: SC999_INST003
          FOV boresight:  0.000000  0.000000  1.000000
            FOV corners:
                          0.010472  0.001745  0.999944
                         -0.010472  0.001745  0.999944
                         -0.010472 -0.001745  0.999944
                          0.010472 -0.001745  0.999944
          --------------------------------------
          Instrument ID: -999004
              FOV shape: POLYGON
              FOV frame: SC999_INST004
          FOV boresight:  0.000000  1.000000  0.000000
            FOV corners:
                          0.000000  0.800000  0.500000
                          0.400000  0.800000 -0.200000
                         -0.400000  0.800000 -0.200000
          --------------------------------------

#### Restrictions

       1)  This routine will not operate unless an I-kernel for the
           instrument with the NAIF ID specified in `instid' have been
           loaded via a call to furnsh_c prior to calling this routine and
           this IK contains the specification for the instrument field of
           view consistent with the expectations of this routine.

#### Literature_References

       None.

#### Author_and_Institution

       C.H. Acton          (JPL)
       N.J. Bachman        (JPL)
       J. Diaz del Rio     (ODC Space)
       B.V. Semenov        (JPL)
       F.S. Turner         (JPL)

#### Version

       -CSPICE Version 1.1.0, 17-DEC-2021 (JDR) (NJB)

           Bug fix: now this function does not attempt to modify the output
           strings `shape' and `frame' if the call to the f2c'd routine getfov_
           fails. For safety, in this failure case, a null is placed in the
           first character of each string.

           Bug fix: added missing exception for the boresight vector
           being the zero vector.

           Edited the header to comply with NAIF standard.

           Updated -Particulars to describe the actual condition that
           reference and cross angles values must satisfy.

       -CSPICE Version 1.0.6, 22-MAR-2017 (JDR) (BVS)

          Header updates: made various header changes to make it
          compliant with the SPICE standard header format; updated
          BSIGHT description; added explanation of output boundary
          vector magnitudes; made other minor header corrections.

          Added call to return_c as part of the error tracing.

       -CSPICE Version 1.0.5, 05-FEB-2009 (BVS)

          Header update: added information about required IK keywords;
          replaced old example with a new one more focused on getfov_c and
          IK keywords.

       -CSPICE Version 1.0.4, 27-OCT-2005 (NJB)

          Header update: replaced reference to bodvar_c with
          reference to bodvcd_c.

       -CSPICE Version 1.0.3, 28-DEC-2004 (BVS)

          Fixed typo in the header example.

       -CSPICE Version 1.0.2, 29-JUL-2003 (NJB) (CHA)

          Various header changes were made to improve clarity. Some
          minor header corrections were made.

       -CSPICE Version 1.0.1, 18-DEC-2001 (FST)

          Updated the header of this wrapper to document the changes
          in GETFOV regarding the addition of support for the ANGLES
          specification.

       -CSPICE Version 1.0.0, 13-APR-2000 (FST)

#### Index_Entries

       return instrument's FOV parameters

#### Link to routine getfov_c source file getfov_c.c

    Fri Dec 31 18:41:07 2021