Remote Sensing Hands-On Lesson (IDL) |
Table of ContentsRemote Sensing Hands-On Lesson (IDL) Overview Note About HTML Links References Tutorials Required Readings The Permuted Index Icy API Documentation Kernels Used Icy Modules Used Time Conversion (convtm) Task Statement Learning Goals Approach Solution Solution Meta-Kernel Solution Source Code Solution Sample Output Obtaining Target States and Positions (getsta) Task Statement Learning Goals Approach Solution Solution Meta-Kernel Solution Source Code Solution Sample Output Spacecraft Orientation and Reference Frames (xform) Task Statement Learning Goals Approach Solution Solution Meta-Kernel Solution Source Code Solution Sample Output Computing Sub-spacecraft and Sub-solar Points (subpts) Task Statement Learning Goals Approach Solution Solution Meta-Kernel Solution Source Code Solution Sample Output Intersecting Vectors with a Triaxial Ellipsoid (fovint) Task Statement Learning Goals Approach Solution Solution Meta-Kernel Solution Source Code Solution Sample Output Remote Sensing Hands-On Lesson (IDL)
Overview
Note About HTML Links
In order for the links to be resolved, create a subdirectory called ``lessons'' under the ``doc/html'' directory of the Toolkit tree and copy this document to that subdirectory before loading it into a Web browser. ReferencesTutorials
Name Lesson steps/routines it describes --------------- ----------------------------------------- Time Time Conversion SCLK and LSK Time Conversion SPK Obtaining Ephemeris Data Frames Reference Frames Using Frames Reference Frames PCK Planetary Constants Data CK Spacecraft Orientation DataThese tutorials are available from the NAIF ftp server at JPL:
http://naif.jpl.nasa.gov/naif/tutorials.html Required Readings
Name Lesson steps/routines that it describes --------------- ----------------------------------------- time.req Time Conversion sclk.req SCLK Time Conversion spk.req Obtaining Ephemeris Data frames.req Using Reference Frames pck.req Obtaining Planetary Constants Data ck.req Obtaining Spacecraft Orientation Data naif_ids.req Determining Body ID Codes The Permuted Index
This text document provides a simple mechanism to discover what Icy procedures perform a particular function of interest as well as the name of the source module that contains the procedure. Icy API Documentation
For example, the document
icy/doc/html/icy/cspice_str2et.htmldescribes the cspice_str2et routine. Kernels Used
# FILE NAME TYPE DESCRIPTION -- ------------------------- ---- ------------------------ 1 naif0008.tls LSK Generic LSK 2 cas00084.tsc SCLK Cassini SCLK 3 981005_PLTEPH-DE405S.bsp SPK Solar System Ephemeris 4 020514_SE_SAT105.bsp SPK Saturnian Satellite Ephemeris 5 030201AP_SK_SM546_T45.bsp SPK Cassini Spacecraft SPK 6 cas_v37.tf FK Cassini FK 7 04135_04171pc_psiv2.bc CK Cassini Spacecraft CK 8 cpck05Mar2004.tpc PCK Cassini Project PCK 9 cas_iss_v09.ti IK ISS Instrument KernelThese SPICE kernels are included in the lesson package available from the NAIF server at JPL:
ftp://naif.jpl.nasa.gov/pub/naif/toolkit_docs/Lessons/ Icy Modules Used
CHAPTER EXERCISE FUNCTIONS NON-VOID KERNELS ------- --------- ------------- --------- ------- 1 convtm cspice_furnsh 1,2 cspice_prompt cspice_str2et cspice_etcal cspice_timout cspice_sce2c cspice_sce2s 2 getsta cspice_furnsh cspice_vnorm 1,3-5 cspice_prompt cspice_str2et cspice_spkezr cspice_spkpos cspice_convrt 3 xform cspice_furnsh cspice_vsep 1-8 cspice_str2et cspice_spkezr cspice_sxform cspice_mxvg cspice_spkpos cspice_pxform cspice_mxv cspice_convrt 4 subpts cspice_furnsh 1,3-5,8 cspice_str2et cspice_subpt cspice_subsol 5 fovint cspice_furnsh cspice_dpr 1-9 cspice_str2et cspice_bodn2c cspice_getfov cspice_sincpt cspice_reclat cspice_ilumin cspice_et2lstRefer to the headers of the various procedures listed above, as detailed interface specifications are provided with the source code. Time Conversion (convtm)Task Statement
Learning Goals
Approach
When completing the ``calendar format'' step above, consider using one of two possible methods: cspice_etcal or cspice_timout. SolutionSolution Meta-Kernel
KPL/MK This is the meta-kernel used in the solution of the ``Time Conversion'' task in the Remote Sensing Hands On Lesson. \begindata KERNELS_TO_LOAD = ( 'kernels/lsk/naif0008.tls', 'kernels/sclk/cas00084.tsc' ) \begintext Solution Source Code
PRO convtm ;; ;; Local Parameters ;; METAKR = "convtm.tm" SCLKID = -82 STRLEN = 50 utctim = '' ;; ;; Load the kernels his program requires. ;; Both the spacecraft clock kernel and a ;; leapseconds kernel should be listed in ;; the meta-kernel. ;; cspice_furnsh, METAKR ;; ;; Prompt the user for the input time string. ;; read, utctim, PROMPT="Input UTC Time: " print, "Converting UTC Time: ", utctim ;; ;; Convert utctim to et. ;; cspice_str2et, utctim, et print, FORMAT="(A,F16.3)", " ET Seconds Past J2000: ", et ;; ;; Now convert ET to a formal calendar time ;; string. This can be accomplished in two ;; ways. ;; cspice_etcal, et, calet print, " Calendar ET (cspice_etcal): ", calet ;; ;; Or use cspice_timout for finer control over the ;; output format. The picture below was built ;; by examining the header of cspice_timout. ;; cspice_timout, et , "YYYY-MON-DDTHR:MN:SC ::TDB", $ STRLEN, calet print, " Calendar ET (cspice_timout): ", calet ;; ;; Convert ET to spacecraft clock time. ;; cspice_sce2s, SCLKID, et, sclkst print, " Spacecraft Clock Time: ", sclkst cspice_unload, METAKR END Solution Sample Output
Converting UTC Time: 2004 jun 11 19:32:00 ET Seconds Past J2000: 140254384.185 Calendar ET (cspice_etcal): 2004 JUN 11 19:33:04.184 Calendar ET (cspice_timout): 2004-JUN-11T19:33:04 Spacecraft Clock Time: 1/1465674964.105 Obtaining Target States and Positions (getsta)Task Statement
Learning Goals
Approach
When deciding which SPK files to load, the Toolkit utility ``brief'' may be of some use. ``brief'' is located in the ``icy/exe'' directory for IDL toolkits. Consult its user's guide available in ``icy/doc/brief.ug'' for details. SolutionSolution Meta-Kernel
KPL/MK This is the meta-kernel used in the solution of the ``Obtaining Target States and Positions'' task in the Remote Sensing Hands On Lesson. \begindata KERNELS_TO_LOAD = ( 'kernels/lsk/naif0008.tls', 'kernels/spk/981005_PLTEPH-DE405S.bsp', 'kernels/spk/020514_SE_SAT105.bsp', 'kernels/spk/030201AP_SK_SM546_T45.bsp' ) \begintext Solution Source Code
PRO getsta ;; ;; Local Parameters ;; METAKR = 'getsta.tm' STRLEN = 50 utctim = '' ;; ;; Load the kernels that this program requires. We ;; will need a leapseconds kernel to convert input ;; UTC time strings into ET. We also will need the ;; necessary SPK files with coverage for the bodies ;; in which we are interested. ;; cspice_furnsh, METAKR ;; ;; Prompt the user for the input time string. ;; read, utctim, PROMPT = 'Input UTC Time: ' print, 'Converting UTC Time: ', utctim ;; ;; Convert utctim to et. ;; cspice_str2et, utctim, et print, FORMAT='(A,F16.3)', ' ET seconds past J2000: ', et ;; ;; Compute the apparent state of Phoebe as seen from ;; CASSINI in the J2000 frame. All of the ephemeris ;; readers return states in units of kilometers and ;; kilometers per second. ;; cspice_spkezr, 'PHOEBE' , et , 'J2000', 'LT+S', $ 'CASSINI', state, ltime print, ' Apparent state of Phoebe as seen ' +$ 'from CASSINI in the J2000 ' print, ' frame (km, km/s): ' print, FORMAT='(A,F16.3)', ' X = ', state[0] print, FORMAT='(A,F16.3)', ' Y = ', state[1] print, FORMAT='(A,F16.3)', ' Z = ', state[2] print, FORMAT='(A,F16.3)', ' VX = ', state[3] print, FORMAT='(A,F16.3)', ' VY = ', state[4] print, FORMAT='(A,F16.3)', ' VZ = ', state[5] ;; ;; Compute the apparent position of Earth as seen from ;; CASSINI in the J2000 frame. Note: We could have ;; continued using cspice_spkezr and simply ignored the ;; velocity components. ;; cspice_spkpos, 'EARTH' , et , 'J2000', 'LT+S', $ 'CASSINI', pos, ltime print, ' Apparent position of Earth as ' +$ 'seen from CASSINI in the J2000 ' print, ' frame (km): ' print, FORMAT='(A,F16.3)', ' X = ', pos[0] print, FORMAT='(A,F16.3)', ' Y = ', pos[1] print, FORMAT='(A,F16.3)', ' Z = ', pos[2] ;; ;; We need only display LT, as it is precisely the ;; light time in which we are interested. ;; print, ' One way light time between CASSINI and ' +$ 'the apparent position' print, FORMAT='(A,F16.3)', ' of Earth (seconds): ', $ ltime ;; ;; Compute the apparent position of the Sun as seen ;; from Phoebe in the J2000 frame. ;; cspice_spkpos, 'SUN' , et , 'J2000', 'LT+S', $ 'PHOEBE', pos, ltime print, ' Apparent position of Sun as seen ' +$ 'from Phoebe in the ' print, ' J2000 frame (km): ' print, FORMAT='(A,F16.3)', ' X = ', pos[0] print, FORMAT='(A,F16.3)', ' Y = ', pos[1] print, FORMAT='(A,F16.3)', ' Z = ', pos[2] ;; ;; Now we need to compute the actual distance between ;; the Sun and Phoebe. The above SPKPOS call gives us ;; the apparent distance, so we need to adjust our ;; aberration correction appropriately. ;; cspice_spkpos, 'SUN' , et , 'J2000', 'NONE', $ 'PHOEBE', pos, ltime ;; ;; Compute the distance between the body centers in ;; kilometers. ;; dist = cspice_vnorm ( pos ) ;; ;; Convert this value to AU using cspice_convrt. ;; Recall, cspice_convrt cannot overwrite the ;; input with the output. Use 'dist_au' for the ;; output value. ;; cspice_convrt, dist, 'KM', 'AU', dist_au print, ' Actual distance between Sun and Phoebe ' + $ 'body centers:' print, FORMAT='(A,F16.3)', ' (AU): ', dist_au cspice_kclear END Solution Sample Output
Converting UTC Time: 2004 JUN 11 19:32:00 ET seconds past J2000: 140254384.185 Apparent state of Phoebe as seen from CASSINI in the J2000 frame (km, km/s): X = -119.921 Y = 2194.139 Z = -57.639 VX = -5.980 VY = -2.119 VZ = -0.295 Apparent position of Earth as seen from CASSINI in the J2000 frame (km): X = 353019393.123 Y = -1328180352.140 Z = -568134171.697 One way light time between CASSINI and the apparent position of Earth (seconds): 4960.427 Apparent position of Sun as seen from Phoebe in the J2000 frame (km): X = 376551465.272 Y = -1190495630.303 Z = -508438699.110 Actual distance between Sun and Phoebe body centers: (AU): 9.012 Spacecraft Orientation and Reference Frames (xform)Task Statement
Learning Goals
Approach
You may find it useful to consult the permuted index, the headers of various source modules, and the following toolkit documentation:
SolutionSolution Meta-Kernel
KPL/MK This is the meta-kernel used in the solution of the ``Spacecraft Orientation and Reference Frames'' task in the Remote Sensing Hands On Lesson. \begindata KERNELS_TO_LOAD = ( 'kernels/lsk/naif0008.tls', 'kernels/sclk/cas00084.tsc', 'kernels/spk/981005_PLTEPH-DE405S.bsp', 'kernels/spk/020514_SE_SAT105.bsp', 'kernels/spk/030201AP_SK_SM546_T45.bsp', 'kernels/fk/cas_v37.tf', 'kernels/ck/04135_04171pc_psiv2.bc', 'kernels/pck/cpck05Mar2004.tpc' ) \begintext Solution Source Code
PRO xform ;; ;; Local Parameters ;; METAKR = 'xform.tm' STRLEN = 50 utctim = '' ;; ;; Load the kernels that this program requires. We ;; will need: ;; ;; A leapseconds kernel ;; A spacecraft clock kernel for CASSINI ;; The necessary ephemerides ;; A planetary constants file (PCK) ;; A spacecraft orientation kernel for CASSINI (CK) ;; A frame kernel (TF) ;; cspice_furnsh, METAKR ;; ;; Prompt the user for the input time string. ;; read, utctim, PROMPT = 'Input UTC Time: ' print, 'Converting UTC Time: ', utctim ;; ;; Convert utctim to et. ;; cspice_str2et, utctim, et print, FORMAT='(A,F16.3)', ' ET seconds past J2000: ', et ;; ;; Compute the apparent state of Phoebe as seen from ;; CASSINI in the J2000 frame. All of the ephemeris ;; readers return states in units of kilometers and ;; kilometers per second. ;; cspice_spkezr, 'PHOEBE' , et , 'J2000', 'LT+S', $ 'CASSINI', state, ltime ;; ;; Now obtain the transformation from the inertial ;; J2000 frame to the non-inertial body-fixed IAU_PHOEBE ;; frame. Since we want the apparent state in the ;; IAU_PHOEBE reference frame, we need to correct the ;; orientation and angular velocity of this frame ;; for one-way light time; hence we subtract ltime from ;; et in the call below. ;; cspice_sxform, 'J2000', 'IAU_PHOEBE', et-ltime, sxfmat ;; ;; Now transform the apparent J2000 state into IAU_PHOEBE ;; with the following matrix multiplication: ;; bfixst = transpose(sxfmat) # state ;; ;; Display the results. ;; print, ' Apparent state of Phoebe as seen ' +$ 'from CASSINI in the IAU_PHOEBE' print, ' body-fixed frame (km, km/s):' print, FORMAT='(A,F19.6)', ' X = ', bfixst[0] print, FORMAT='(A,F19.6)', ' Y = ', bfixst[1] print, FORMAT='(A,F19.6)', ' Z = ', bfixst[2] print, FORMAT='(A,F19.6)', ' VX = ', bfixst[3] print, FORMAT='(A,F19.6)', ' VY = ', bfixst[4] print, FORMAT='(A,F19.6)', ' VZ = ', bfixst[5] ;; ;; It is worth pointing out, all of the above could ;; have been done with a single use of cspice_spkezr: ;; ;; cspice_spkezr, 'PHOEBE' , et , 'IAU_PHOEBE', 'LT+S', $ 'CASSINI', state, ltime ;; ;; Display the results. ;; print, ' Apparent state of Phoebe as seen ' +$ 'from CASSINI in the IAU_PHOEBE' print, ' body-fixed frame (km, km/s) ' +$ 'obtained using cspice_spkezr' print, ' directly:' print, FORMAT='(A,F19.6)', ' X = ', state[0] print, FORMAT='(A,F19.6)', ' Y = ', state[1] print, FORMAT='(A,F19.6)', ' Z = ', state[2] print, FORMAT='(A,F19.6)', ' VX = ', state[3] print, FORMAT='(A,F19.6)', ' VY = ', state[4] print, FORMAT='(A,F19.6)', ' VZ = ', state[5] ;; ;; Note that the velocity found by using cspice_spkezr ;; to compute the state in the IAU_PHOEBE frame differs ;; at the few mm/second level from that found previously ;; by calling cspice_spkezr and then cspice_sxform. Computing ;; velocity via a single call to cspice_spkezr as we've ;; done immediately above is slightly more accurate because ;; it accounts for the effect of the rate of change of ;; light time on the apparent angular velocity of the ;; target's body-fixed reference frame. ;; ;; Now we are to compute the angular separation between ;; the apparent position of the Earth as seen from the ;; orbiter and the nominal boresight of the high gain ;; antenna. First, compute the apparent position of ;; the Earth as seen from CASSINI in the J2000 frame. ;; cspice_spkpos, 'EARTH' , et, 'J2000', 'LT+S', $ 'CASSINI', pos, ltime ;; ;; Now compute the location of the antenna boresight ;; at this same epoch. From reading the frame kernel ;; we know that the antenna boresight is nominally the ;; +Z axis of the CASSINI_HGA frame defined there. ;; bsight = [ 0.D0, 0.D0, 1.D0] ;; ;; Now compute the rotation matrix from CASSINI_HGA into ;; J2000. ;; cspice_pxform, 'CASSINI_HGA', 'J2000', et, pform ;; ;; And multiply the result to obtain the nominal ;; antenna boresight in the J2000 reference frame. ;; cspice_mxv, pform, bsight, bsight ;; ;; Lastly compute the angular separation. ;; cspice_convrt, cspice_vsep(bsight, pos), 'RADIANS', $ 'DEGREES', sep print, ' Angular separation between the ' +$ 'apparent position of' print, ' Earth and the CASSINI high ' +$ 'gain antenna boresight (degrees):' print, FORMAT='(A,F16.3)', ' ', sep ;; ;; Or alternatively we can work in the antenna ;; frame directly. ;; cspice_spkpos, 'EARTH' , et , 'CASSINI_HGA', 'LT+S', $ 'CASSINI', pos, ltime ;; ;; The antenna boresight is the Z-axis in the ;; CASSINI_HGA frame. ;; bsight = [ 0.D0, 0.D0, 1.D0] ;; ;; Lastly compute the angular separation. ;; cspice_convrt, cspice_vsep(bsight, pos), 'RADIANS', $ 'DEGREES', sep print, ' Angular separation between the ' +$ 'apparent position of' print, ' Earth and the CASSINI high ' +$ 'gain antenna boresight computed' print, ' using vectors in the CASSINI_HGA ' +$ 'frame (degrees):' print, FORMAT='(A,F16.3)', ' ', sep cspice_kclear END Solution Sample Output
Converting UTC Time: 2004 JUN 11 19:32:00 ET seconds past J2000: 140254384.185 Apparent state of Phoebe as seen from CASSINI in the IAU_PHOEBE body-fixed frame (km, km/s): X = -1982.639762 Y = -934.530471 Z = -166.562595 VX = 3.970833 VY = -3.812498 VZ = -2.371663 Apparent state of Phoebe as seen from CASSINI in the IAU_PHOEBE body-fixed frame (km, km/s) obtained using cspice_spkezr directly: X = -1982.639762 Y = -934.530471 Z = -166.562595 VX = 3.970832 VY = -3.812496 VZ = -2.371663 Angular separation between the apparent position of Earth and the CASSINI high gain antenna boresight (degrees): 71.924 Angular separation between the apparent position of Earth and the CASSINI high gain antenna boresight computed using vectors in the CASSINI_HGA frame (degrees): 71.924 Computing Sub-spacecraft and Sub-solar Points (subpts)Task Statement
Learning Goals
Approach
One point worth considering: Which method do you want to use to compute the sub-solar (or sub-observer) point? SolutionSolution Meta-Kernel
KPL/MK This is the meta-kernel used in the solution of the ``Computing Sub-spacecraft and Sub-solar Points'' task in the Remote Sensing Hands On Lesson. \begindata KERNELS_TO_LOAD = ( 'kernels/lsk/naif0008.tls', 'kernels/spk/981005_PLTEPH-DE405S.bsp', 'kernels/spk/020514_SE_SAT105.bsp', 'kernels/spk/030201AP_SK_SM546_T45.bsp', 'kernels/pck/cpck05Mar2004.tpc' ) \begintext Solution Source Code
PRO subpts ;; ;; Local Parameters ;; METAKR = 'subpts.tm' STRLEN = 50 utctim = '' ;; ;; Load the kernels that this program requires. We ;; will need: ;; ;; A leapseconds kernel ;; The necessary ephemerides ;; A planetary constants file (PCK) ;; cspice_furnsh, METAKR ;; ;; Prompt the user for the input time string. ;; read, utctim, PROMPT = 'Input UTC Time: ' print, 'Converting UTC Time: ', utctim ;; ;; Convert utctim to et. ;; cspice_str2et, utctim, et print, FORMAT='(A,F16.3)', ' ET seconds past J2000: ', et ;; ;; Compute the apparent sub-observer point of CASSINI ;; on Phoebe. ;; cspice_subpnt, 'NEAR POINT: ELLIPSOID', $ 'PHOEBE', et, 'IAU_PHOEBE', 'LT+S', $ 'CASSINI', spoint, trgepc, srfvec print, ' Apparent sub-observer point of CASSINI ' +$ 'on Phoebe in the' print, ' IAU_PHOEBE frame (km):' print, FORMAT='(A,F16.3)', ' X = ', spoint[0] print, FORMAT='(A,F16.3)', ' Y = ', spoint[1] print, FORMAT='(A,F16.3)', ' Z = ', spoint[2] print, FORMAT='(A,F16.3)', ' ALT = ', cspice_vnorm(srfvec) ;; ;; Compute the apparent sub-solar point on Phoebe ;; as seen from CASSINI. ;; cspice_subslr, 'NEAR POINT: ELLIPSOID', $ 'PHOEBE', et, 'IAU_PHOEBE', 'LT+S', $ 'CASSINI', spoint, trgepc, srfvec print, ' Apparent sub-solar point on Phoebe ' +$ 'as seen from CASSINI in' print, ' the IAU_PHOEBE frame (km):' print, FORMAT='(A,F16.3)', ' X = ', spoint[0] print, FORMAT='(A,F16.3)', ' Y = ', spoint[1] print, FORMAT='(A,F16.3)', ' Z = ', spoint[2] cspice_unload, METAKR END Solution Sample Output
Converting UTC Time: 2004 JUN 11 19:32:00 ET seconds past J2000: 140254384.185 Apparent sub-observer point of CASSINI on Phoebe in the IAU_PHOEBE frame (km): X = 104.498 Y = 45.269 Z = 7.383 ALT = 2084.116 Apparent sub-solar point on Phoebe as seen from CASSINI in the IAU_PHOEBE frame (km): X = 78.681 Y = 76.879 Z = -21.885 Intersecting Vectors with a Triaxial Ellipsoid (fovint)Task Statement
At each point of intersection compute the following:
Use this program to compute values at the epoch:
Learning Goals
Approach
SolutionSolution Meta-Kernel
KPL/MK This is the meta-kernel used in the solution of the ``Intersecting Vectors with a Triaxial Ellipsoid'' task in the Remote Sensing Hands On Lesson. \begindata KERNELS_TO_LOAD = ( 'kernels/lsk/naif0008.tls', 'kernels/sclk/cas00084.tsc', 'kernels/spk/981005_PLTEPH-DE405S.bsp', 'kernels/spk/020514_SE_SAT105.bsp', 'kernels/spk/030201AP_SK_SM546_T45.bsp', 'kernels/fk/cas_v37.tf', 'kernels/ck/04135_04171pc_psiv2.bc', 'kernels/pck/cpck05Mar2004.tpc', 'kernels/ik/cas_iss_v09.ti' ) \begintext Solution Source Code
PRO fovint ;; ;; Local Parameters ;; METAKR = 'fovint.tm' STRLEN = 50 BCVLEN = 5 utctim = '' scan_vecs = dblarr( 3, BCVLEN ) vecnam = ['Boundary Corner 1', $ 'Boundary Corner 2', $ 'Boundary Corner 3', $ 'Boundary Corner 4', $ 'Cassini NAC Boresight' ] ;; ;; Load the kernels that this program requires. We ;; will need: ;; ;; A leapseconds kernel. ;; A SCLK kernel for CASSINI. ;; Any necessary ephemerides. ;; The CASSINI frame kernel. ;; A CASSINI C-kernel. ;; A PCK file with Phoebe constants. ;; The CASSINI ISS I-kernel. ;; cspice_furnsh, METAKR ;; ;; Prompt the user for the input time string. ;; read, utctim, PROMPT = 'Input UTC Time: ' print, 'Converting UTC Time: ', utctim ;; ;; Convert utctim to et. ;; cspice_str2et, utctim, et print, FORMAT='(A,F16.3)', ' ET seconds past J2000: ', et ;; ;; Now we need to obtain the FOV configuration of ;; the ISS NAC camera. To do this we will need the ;;ID code for CASSINI_ISS_NAC. ;; cspice_bodn2c, 'CASSINI_ISS_NAC', nacid, found ;; ;; Stop the program if the code was not found. ;; if ( ~ found ) then begin print, 'Unable to locate the ID code for ' +$ 'CASSINI_ISS_NAC' return endif ;; ;; Now retrieve the field of view parameters. ;; cspice_getfov, nacid, BCVLEN, shape, insfrm, bsight, bounds ;; ;; Rather than treat 'bsight' as a separate vector, ;; copy it and 'bounds to 'scan_vecs'. ;; scan_vecs[ 0:11] = bounds[0:11] scan_vecs[12:14] = bsight[0:2] ;; ;; Now perform the same set of calculations for each ;; vector listed in the 'bounds' array. ;; for i=0, 4 do begin ;; ;; Call sincpt to determine coordinates of the ;; intersection of this vector with the surface ;; of Phoebe. ;; cspice_sincpt, 'Ellipsoid', 'PHOEBE', et, $ 'IAU_PHOEBE', 'LT+S', 'CASSINI', $ insfrm, scan_vecs[*,i], point, $ trgepc, srfvec, found ;; ;; Check the found flag. Display a message if ;; the point of intersection was not found, ;; otherwise continue with the calculations. ;; print, 'Vector: ', vecnam[i] if ( ~ found ) then begin print, 'No intersection point found at ' +$ 'this epoch for this vector.' endif else begin ;; ;; Now, we have discovered a point of intersection. ;; Start by displaying the position vector in the ;; IAU_PHOEBE frame of the intersection. ;; print, ' Position vector of surface intercept ' +$ 'in the IAU_PHOEBE frame (km):' print, FORMAT='(A,F16.3)', ' X = ', point[0] print, FORMAT='(A,F16.3)', ' Y = ', point[1] print, FORMAT='(A,F16.3)', ' Z = ', point[2] ;; ;; Display the planetocentric latitude and longitude ;; of the intercept. ;; cspice_reclat, point, radius, lon, lat print, ' Planetocentric coordinates of ' +$ 'the intercept (degrees):' print, FORMAT='(A,F16.3)', ' LAT = ', $ lat * cspice_dpr() print, FORMAT='(A,F16.3)', ' LON = ', $ lon * cspice_dpr() ;; ;; Compute the illumination angles at this ;; point. ;; cspice_ilumin, 'Ellipsoid', 'PHOEBE', et, $ 'IAU_PHOEBE', 'LT+S', 'CASSINI', $ point, trgepc, srfvec, $ phase, solar, emissn print, FORMAT='(A,F16.3)', $ ' Phase angle (degrees): ', $ phase * cspice_dpr() print, FORMAT='(A,F16.3)', $ ' Solar incidence angle (degrees): ', $ solar * cspice_dpr() print, FORMAT='(A,F16.3)', $ ' Emission angle (degrees): ', $ emissn * cspice_dpr() print endelse endfor ;; ;; Lastly compute the local solar time at the boresight ;; intersection. ;; if ( found ) then begin ;; ;; Get Phoebe ID. ;; cspice_bodn2c, 'PHOEBE', phoeid, found ;; ;; Return if the code was not found. ;; if ( ~found ) then begin print, 'Unable to locate the ID code for Phoebe.' return endif ;; ;; Compute local solar time corresponding to ;; the TDB light time corrected epoch at the intercept. ;; cspice_et2lst, trgepc, phoeid, lon, 'PLANETOCENTRIC', $ hr, min, sc, time, ampm print, ' Local Solar Time at boresight ' +$ 'intercept (24 Hour Clock):' print, ' ' + time endif else begin print, ' No boresight intercept to compute ' +$ 'local solar time.' endelse cspice_kclear END Solution Sample Output
Converting UTC Time: 2004 JUN 11 19:32:00 ET seconds past J2000: 140254384.185 Vector: Boundary Corner 1 Position vector of surface intercept in the IAU_PHOEBE frame (km): X = 91.026 Y = 67.190 Z = 2.030 Planetocentric coordinates of the intercept (degrees): LAT = 1.028 LON = 36.433 Phase angle (degrees): 28.110 Solar incidence angle (degrees): 16.121 Emission angle (degrees): 14.627 Vector: Boundary Corner 2 Position vector of surface intercept in the IAU_PHOEBE frame (km): X = 89.991 Y = 66.726 Z = 14.733 Planetocentric coordinates of the intercept (degrees): LAT = 7.492 LON = 36.556 Phase angle (degrees): 27.894 Solar incidence angle (degrees): 22.894 Emission angle (degrees): 14.988 Vector: Boundary Corner 3 Position vector of surface intercept in the IAU_PHOEBE frame (km): X = 80.963 Y = 76.643 Z = 14.427 Planetocentric coordinates of the intercept (degrees): LAT = 7.373 LON = 43.430 Phase angle (degrees): 28.171 Solar incidence angle (degrees): 21.315 Emission angle (degrees): 21.977 Vector: Boundary Corner 4 Position vector of surface intercept in the IAU_PHOEBE frame (km): X = 81.997 Y = 77.106 Z = 1.699 Planetocentric coordinates of the intercept (degrees): LAT = 0.865 LON = 43.239 Phase angle (degrees): 28.385 Solar incidence angle (degrees): 13.882 Emission angle (degrees): 21.763 Vector: Cassini NAC Boresight Position vector of surface intercept in the IAU_PHOEBE frame (km): X = 86.390 Y = 72.089 Z = 8.255 Planetocentric coordinates of the intercept (degrees): LAT = 4.196 LON = 39.844 Phase angle (degrees): 28.139 Solar incidence angle (degrees): 18.247 Emission angle (degrees): 17.858 Local Solar Time at boresight intercept (24 Hour Clock): 11:31:50 |