getfov_c |

Table of contents## Proceduregetfov_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] ) ## AbstractReturn the field-of-view (FOV) parameters for a specified instrument. The instrument is specified by its NAIF ID code. ## Required_ReadingNAIF_IDS ## KeywordsFOV INSTRUMENT ## Brief_I/OVARIABLE 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_Inputinstid 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_Outputshape 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.) ## ParametersMINCOS 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. ## Exceptions1) 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. ## FilesThis routine relies upon having successfully loaded an instrument kernel (IK file) via the routine furnsh_c prior to calling this routine. ## ParticularsThis 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. ## ExamplesThe 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++ ) { ## Restrictions1) 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_ReferencesNone. ## Author_and_InstitutionC.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 ## Index_Entriesreturn instrument's FOV parameters |

Fri Dec 31 18:41:07 2021