cspice_ilumin |
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## AbstractCSPICE_ILUMIN computes the illumination angles (phase, solar incidence, and emission) at a specified surface point of a target body. This routine supersedes cspice_illum, which doesn't have an input argument for the target body-fixed frame name. For important details concerning this module's function, please refer to the CSPICE routine ilumin_c. ## I/OGiven: method a scalar string providing parameters defining the computation method to be used. Parameters include, but are not limited to, the shape model used to represent the surface of the target body. The only choice currently supported is '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. Neither case nor white space are significant in 'method'. For example, the string ' eLLipsoid ' is valid. target the scalar string 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. et the scalar double precision epoch, specified in ephemeris seconds past J2000, at which the apparent illumination angles at the specified surface point on the target body, as seen from the observing body, are to be computed. fixref the scalar string naming the body-fixed, body-centered reference frame associated with the target body. The input surface point `spoint' and the output vector 'srfvec' are expressed relative to this reference frame. 'fixref' is case-insensitive, and leading and trailing blanks are not significant. abcorr the scalar string aberration correction to use in computing the location of the surface point, the orientation of the target body, and the location of the Sun. For remote sensing applications, where the apparent illumination angles seen by the observer are desired, normally either of the corrections 'LT+S' 'CN+S' should be used. These and the other supported options are described below. 'abcorr' may be any of the following: 'NONE' No aberration correction. 'LT' Correct the position of the input surface point SPOINT and orientation of target body for light time, and correct the position of the Sun as seen from the target for light time. 'LT+S' Correct the position of the surface point SPOINT for light time and stellar aberration, correct the orientation of the target body for light time, and correct the position of the Sun as seen from the target for light time and stellar aberration. 'CN' Converged Newtonian light time correction. In solving the light time equation, the 'CN' correction iterates until the solution converges. Both the position of the surface point SPOINT c and rotation of the target body, as well as the position of the Sun as seen from the target, are corrected for light time. 'CN+S' Converged Newtonian light time and stellar aberration corrections. This option produces a solution that is at least as accurate at that obtainable with the 'LT+S' option. Whether the 'CN+S' solution is substantially more accurate 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. Neither case nor white space are significant in 'abcorr'. For example, the string 'Lt + s' is valid. obsrvr the scalar string 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. 'obsrvr' may be not be identical to 'target'. spoint a double precision 3-vector defining the surface point on the target body, expressed in Cartesian coordinates, relative to the body-fixed target frame designated by 'fixref'. 'spoint' need not be visible from the observer's location at the epoch ET. The components of 'spoint' have units of km. the call: ## ExamplesAny numerical results shown for this example may differ between platforms as the results depend on the SPICE kernels used as input and the machine specific arithmetic implementation. Find the phase, solar incidence, and emission angles at the sub-solar and sub-spacecraft points on Mars as seen from the Mars Global Surveyor spacecraft at a user-specified UTC time. Use light time and stellar aberration corrections. ;; ;; Load kernel files. ;; cspice_furnsh, 'standard.tm' cspice_furnsh, '/kernels/MGS/spk/mgs_ext13_ipng_mgs95j.bsp' ;; ;; Convert the UTC request time to ET (seconds past J2000 TDB). ;; utc = '2004 JAN 1 12:00:00' cspice_str2et, utc, et ;; ;; Assign observer and target names. The acronym MGS ;; indicates Mars Global Surveyor. See NAIF_IDS for a ;; list of names recognized by SPICE. Also set the ;; aberration correction flag. ;; target = 'Mars' obsrvr = 'MGS' abcorr = 'CN+S' ;; ;; Find the sub-solar point on the Earth as seen from ;; the MGS spacecraft at et. Use the 'near point' ;; style of sub-point definition. ;; cspice_subslr, 'near point: ellipsoid', $ target, et, 'iau_mars', abcorr, $ obsrvr, ssolpt, trgepc, srfvec ;; ;; Now find the sub-spacecraft point. ;; cspice_subpnt, 'near point: ellipsoid', $ target, et, 'iau_mars', abcorr, $ obsrvr, sscpt, trgepc, srfvec ;; ;; Find the phase, solar incidence, and emission ;; angles at the sub-solar point on the Earth as seen ;; from MGS at time et. ;; ## ParticularsNone. ## Required ReadingICY.REQ FRAMES.REQ PCK.REQ SPK.REQ TIME.REQ ## Version-Icy Version 1.0.3, 11-NOV-2013, SCK (JPL) References to the new 'cspice_pxfrm2' routine were added to the 'I/O returns' section. A problem description was added to the 'Examples' section. -Icy Version 1.0.2, 13-JUN-2010, EDW (JPL) Minor edit to code comments eliminating typo. -Icy Version 1.0.1, 10-NOV-2008, EDW (JPL) Edited I/O section; added 'fixref' description. -Icy Version 1.0.0, 11-FEB-2008, EDW (JPL) ## Index_Entriesillumination angles lighting angles phase angle emission angle solar incidence angle |

Wed Apr 5 17:58:02 2017