subsol_c |

Table of contents## Proceduresubsol_c ( Sub-solar point ) void subsol_c ( ConstSpiceChar * method, ConstSpiceChar * target, SpiceDouble et, ConstSpiceChar * abcorr, ConstSpiceChar * obsrvr, SpiceDouble spoint[3] ) ## AbstractDeprecated: This routine has been superseded by the CSPICE routine subslr_c. This routine is supported for purposes of backward compatibility only. Determine the coordinates of the sub-solar point on a target body as seen by a specified observer at a specified epoch, optionally corrected for planetary (light time) and stellar aberration. ## Required_ReadingFRAMES PCK SPK TIME ## KeywordsGEOMETRY ## Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- method I Computation method. target I Name of target body. et I Epoch in ephemeris seconds past J2000 TDB. abcorr I Aberration correction. obsrvr I Name of observing body. spoint O Sub-solar point on the target body. ## Detailed_Inputmethod is a short string specifying the computation method to be used. The choices are: "Near point" The sub-solar point is defined as the nearest point on the target to the sun. "Intercept" The sub-observer point is defined as the target surface intercept of the line containing the target's center and the sun's center. In both cases, the intercept computation treats the surface of the target body as a triaxial ellipsoid. The ellipsoid's radii must be available in the kernel pool. Neither case nor white space are significant in method. For example, the string " NEARPOINT" is valid. target is the name of the target body. `target' is case-insensitive, and leading and trailing blanks in `target' are not significant. Optionally, you may supply a string containing the integer ID code for the object. For example both "MOON" and "301" are legitimate strings that indicate the moon is the target body. This routine assumes that the target body is modeled by a tri-axial ellipsoid, and that a PCK file containing its radii has been loaded into the kernel pool via furnsh_c. et is the epoch in ephemeris seconds past J2000 at which the sub-solar point on the target body is to be computed. abcorr indicates the aberration corrections to be applied when computing the observer-target state. abcorr may be any of the following. "NONE" Apply no correction. Return the geometric sub-solar point on the target body. "LT" Correct for planetary (light time) aberration. Both the state and rotation of the target body are corrected for one way light time from target to observer. The state of the sun relative to the target is corrected for one way light from the sun to the target; this state is evaluated at the epoch obtained by retarding et by the one way light time from target to observer. "LT+S" Correct for planetary (light time) and stellar aberrations. Light time corrections are the same as in the "LT" case above. The target state is additionally corrected for stellar aberration as seen by the observer, and the sun state is corrected for stellar aberration as seen from the target. "CN" Converged Newtonian light time correction. In solving the light time equation, the "CN" correction iterates until the solution converges (three iterations on all supported platforms). Whether the "CN+S" solution is substantially more accurate than the "LT" solution depends on the geometry of the participating objects and on the accuracy of the input data. In all cases this routine will execute more slowly when a converged solution is computed. See the -Particulars section below for a discussion of precision of light time corrections. Light time corrections are applied as in the "LT" case. "CN+S" Converged Newtonian light time correction and stellar aberration correction. Light time and stellar aberration corrections are applied as in the "LT+S" case. obsrvr is the name of the observing body. This is typically a spacecraft, the earth, or a surface point on the earth. `obsrvr' is case-insensitive, and leading and trailing blanks in `obsrvr' are not significant. Optionally, you may supply a string containing the integer ID code for the object. For example both "EARTH" and "399" are legitimate strings that indicate the earth is the observer. ## Detailed_Outputspoint is the sub-solar point on the target body at et, expressed relative to the body-fixed frame of the target body. The sub-solar point is defined either as the point on the target body that is closest to the sun, or the target surface intercept of the line containing the sun's center and the target's center; the input argument method selects the definition to be used. The body-fixed frame, which is time-dependent, is evaluated at et if abcorr is "NONE"; otherwise the frame is evaluated at et-lt, where lt is the one way light time from target to observer. The state of the target body is corrected for aberration as specified by abcorr; the corrected state is used in the geometric computation. As indicated above, the rotation of the target is retarded by one way light time if abcorr specifies that light time correction is to be done. The state of the sun as seen from the target body body is also corrected for aberration as specified by abcorr. The corrections, when selected, are applied at the epoch et-lt, where lt is the one way light time from target to observer. ## ParametersNone. ## ExceptionsIf any of the listed errors occur, the output arguments are left unchanged. 1) If the input argument `method' is not recognized, the error SPICE(DUBIOUSMETHOD) is signaled by a routine in the call tree of this routine. 2) If either of the input body names `target' or `obsrvr' cannot be mapped to NAIF integer codes, the error SPICE(IDCODENOTFOUND) is signaled by a routine in the call tree of this routine. 3) If `obsrvr' and `target' map to the same NAIF integer ID codes, the error SPICE(BODIESNOTDISTINCT) is signaled by a routine in the call tree of this routine. 4) If frame definition data enabling the evaluation of the state of the target relative to the observer in target body-fixed coordinates have not been loaded prior to calling ## FilesAppropriate SPK, PCK, and frame data must be available to the calling program before this routine is called. Typically the data are made available by loading kernels; however the data may be supplied via subroutine interfaces if applicable. The following data are required: - SPK data: ephemeris data for sun, target, and observer must be loaded. If aberration corrections are used, the states of sun, target, and observer relative to the solar system barycenter must be calculable from the available ephemeris data. Ephemeris data are made available by loading one or more SPK files via furnsh_c. - PCK data: triaxial radii for the target body must be loaded into the kernel pool. Typically this is done by loading a text PCK file via furnsh_c. - Further PCK data: a rotation model for the target body must be loaded. This may be provided in a text or binary PCK file which is loaded via furnsh_c. - Frame data: if a frame definition is required to convert the sun, observer, and target states to the body-fixed frame of the target, that definition must be available in the kernel pool. Typically the definition is supplied by loading a frame kernel via furnsh_c. In all cases, kernel data are normally loaded once per program run, NOT every time this routine is called. ## Particulars
## 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) Find the sub-solar point on Mars as seen from the Mars Global Surveyor (MGS) spacecraft for a specified time. Perform the computation twice, using both the "intercept" and "near point" options. Use the meta-kernel shown below to load the required SPICE kernels. KPL/MK File: subsol_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 --------- -------- de430.bsp Planetary ephemeris mar097.bsp Mars satellite ephemeris pck00010.tpc Planet orientation and radii naif0011.tls Leapseconds mgs_ext12_ipng_mgs95j.bsp MGS ephemeris \begindata KERNELS_TO_LOAD = ( 'de430.bsp', 'mar097.bsp', 'pck00010.tpc', 'naif0011.tls', 'mgs_ext12_ipng_mgs95j.bsp') \begintext End of meta-kernel Example code begins here. /. Program subsol_ex1 ./ #include <stdio.h> #include "SpiceUsr.h" int main( void ) { #define METHLN 26 SpiceChar method [2][ METHLN ] = { "Intercept", "Near point" }; SpiceDouble et; SpiceDouble lat; SpiceDouble lon; SpiceDouble radius; SpiceDouble spoint[3]; SpiceInt i; /. Load kernel files. ./ furnsh_c ( "subsol_ex1.tm" ); /. Convert the UTC request time to ET (seconds past J2000, TDB). ./ str2et_c ( "2003 OCT 13 06:00:00 UTC", &et ); /. Compute sub-spacecraft point using light time and stellar aberration corrections. Use the "target surface intercept" definition of sub-spacecraft point on the first loop iteration, and use the "near point" definition on the second. ./ for ( i = 0; i < 2; i++ ) { ## Restrictions1) The appropriate kernel data must have been loaded before this routine is called. See the -Files section above. ## Literature_ReferencesNone. ## Author_and_InstitutionN.J. Bachman (JPL) J. Diaz del Rio (ODC Space) J.E. McLean (JPL) B.V. Semenov (JPL) ## Version-CSPICE Version 1.0.6, 01-NOV-2021 (JDR) Edited the header to comply with NAIF standard. Updated example to use a meta-kernel to load the required kernels. Added example's problem statement and solution. -CSPICE Version 1.0.5, 10-JUL-2014 (NJB) Discussion of light time corrections was updated. Assertions that converged light time corrections are unlikely to be useful were removed. -CSPICE Version 1.0.4, 19-MAY-2010 (BVS) Index line now states that this routine is deprecated. -CSPICE Version 1.0.3, 07-FEB-2008 (NJB) -Abstract now states that this routine is deprecated. -CSPICE Version 1.0.2, 22-JUL-2004 (NJB) Updated header to indicate that the `target' and `observer' input arguments can now contain string representations of integers. Deleted references to kernel-specific loaders. Made miscellaneous minor corrections to header comments. -CSPICE Version 1.0.1, 12-DEC-2002 (NJB) Corrected and updated code example in header. -CSPICE Version 1.0.0, 03-SEP-1999 (NJB) (JEM) ## Index_EntriesDEPRECATED sub-solar point |

Fri Dec 31 18:41:13 2021