Geometric Event Finding Hands-On Lesson, using MEX (FORTRAN) |
Table of ContentsGeometric Event Finding Hands-On Lesson, using MEX (FORTRAN) Overview Note About HTML Links References Tutorials Required Readings The Permuted Index API Documentation Kernels Used SPICE Modules Used Find View Periods Task Statement Learning Goals Approach Solution steps Solution Solution Meta-Kernel Solution Code Solution Sample Output Find Times when Target is Visible Task Statement Learning Goals Approach Solution steps Solution Solution Meta-Kernel Solution Code Solution Sample Output Extra Credit Task statements Solutions Geometric Event Finding Hands-On Lesson, using MEX (FORTRAN)
Overview
In this lesson the student is asked to construct a program that finds the time intervals, within a specified time range, when the Mars Express Orbiter (MEX) is visible from the DSN station DSS-14. Possible occultation of the spacecraft by Mars is to be considered. Note About HTML Links
In order for the links to be resolved, if not done already by installing the lessons package under the Toolkit's ``doc/html'' directory, 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. References
Of these documents, the ``Tutorials'' contains the highest level descriptions with the least number of details while the ``Required Reading'' documents contain much more detailed specifications. The most complete specifications are provided in the ``API Documentation''. In some cases the lesson explanations also refer to the information provided in the meta-data area of the kernels used in the lesson examples. It is especially true in case of the FK and IK files, which often contain comprehensive descriptions of the frames, instrument FOVs, etc. Since both FK and IK are text kernels, the information provided in them can be viewed using any text editor, while the meta information provided in binary kernels -- SPKs and CKs -- can be viewed using ``commnt'' or ``spacit'' utility programs located in ``toolkit/exe'' of Toolkit installation tree. Tutorials
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 Lunar-Earth PCK Lunar and Earth Orientation Data GF The SPICE Geometry Finder (GF) subsystem DSK Detailed Target Shape (Topography) DataThese tutorials are available from the NAIF server at JPL:
https://naif.jpl.nasa.gov/naif/tutorials.html Required Readings
Name Lesson steps/routines that it describes --------------- ----------------------------------------- cells.req Cell/window initialization frames.req Using reference frames gf.req The SPICE geometry finder (GF) subsystem kernel.req Loading SPICE kernels naif_ids.req Body and reference frame names pck.req Obtaining planetary constants data spk.req Computing positions and velocities time.req UTC to ET time conversion windows.req The SPICE window data type The Permuted Index
This text document provides a simple mechanism by which users can discover which SPICE routines perform functions of interest, as well as the names of the source files that contain these routines. It is particularly useful for FORTRAN programmers because some of the routines are entry points; the names of these routines do not translate directly into the name of the respective source files that contain them. API Documentation
For example the path of the source code of the STR2ET routine is
toolkit/src/spicelib/str2et.forSince some of the FORTRAN routines are entry points they may be part of a source file that has different name. The ``Permuted Index'' document mentioned above can be used to locate the name of their source file. Kernels Used
# FILE NAME TYPE DESCRIPTION -- ------------------------------ ---- ------------------------------ 1 de405xs.bsp SPK Planetary ephemeris SPK, subsetted to cover only time range of interest 2 earthstns_itrf93_050714.bsp SPK DSN station SPK 3 earth_topo_050714.tf FK DSN station frame definitions 4 earth_000101_060525_060303.bpc PCK Binary PCK for Earth 5 naif0008.tls LSK Generic LSK 6 ORMM__040501000000_00076XS.BSP SPK MEX Orbiter trajectory SPK, subsetted to cover only time range of interest 7 pck00008.tpc PCK Generic PCK 8 mars_lowres.bds DSK Low-resolution Mars DSKThese SPICE kernels are included in the lesson package. SPICE Modules Used
CHAPTER EXERCISE ROUTINES FUNCTIONS KERNELS ------- --------- --------- --------- ---------- 1 viewpr FURNSH RPD 1-7 TOSTDO WNCARD REPMC REPMF STR2ET TIMOUT SSIZED WNINSD GFPOSC WNFETD 2 visibl FURNSH RPD 1-8 TOSTDO WNCARD REPMC REPMF STR2ET TIMOUT SSIZED WNINSD GFPOSC GFOCLT WNDIFD WNFETD extra (*) GFDIST 1,5-7 KCLEAR (*) Additional APIs and kernels used in Extra Credit tasks.Refer to the headers of the various routines listed above, as detailed interface specifications are provided with the source code. Find View PeriodsTask Statement
2004 MAY 2 TDB 2004 MAY 6 TDBwhen the Mars Express Orbiter (MEX) is visible from the DSN station DSS-14. These time intervals are frequently called ``view periods.'' The spacecraft is considered visible if its apparent position (that is, its position corrected for light time and stellar aberration) has elevation of at least 6 degrees in the topocentric reference frame DSS-14_TOPO. In this exercise, we ignore the possibility of occultation of the spacecraft by Mars. Use a search step size that ensures that no view periods of duration 5 minutes or longer will be missed by the search. Display the start and stop times of these intervals using TDB calendar dates and millisecond precision. Learning Goals
ApproachSolution steps
Preparation:
SolutionSolution Meta-Kernel
KPL/MK Example meta-kernel for geometric event finding hands-on coding lesson. Version 2.0.0 13-JUL-2017 (JDR) The names and contents of the kernels referenced by this meta-kernel are as follows: File Name Description ------------------------------ ------------------------------ de405xs.bsp Planetary ephemeris SPK, subsetted to cover only time range of interest. earthstns_itrf93_050714.bsp DSN station SPK. earth_topo_050714.tf DSN station frame definitions. earth_000101_060525_060303.bpc Binary PCK for Earth. naif0008.tls Generic LSK. ORMM__040501000000_00076XS.BSP MEX Orbiter trajectory SPK, subsetted to cover only time range of interest. pck00008.tpc Generic PCK. \begindata KERNELS_TO_LOAD = ( 'kernels/spk/de405xs.bsp' 'kernels/spk/earthstns_itrf93_050714.bsp' 'kernels/fk/earth_topo_050714.tf' 'kernels/pck/earth_000101_060525_060303.bpc' 'kernels/lsk/naif0008.tls' 'kernels/spk/ORMM__040501000000_00076XS.BSP' 'kernels/pck/pck00008.tpc' ) \begintext Solution Code
PROGRAM VIEWPR IMPLICIT NONE C C Find and display the window of times when the MEX C spacecraft is above a specified elevation limit in the C topocentric reference frame of DSN station DSS-14. C C C SPICELIB functions C DOUBLE PRECISION RPD INTEGER WNCARD C C Global GF parameters: we import from this file C the definition of the GF workspace size parameter C C NWMAX C INCLUDE 'gf.inc' C C Local parameters C C Format string for time output: C CHARACTER*(*) TDBFMT PARAMETER ( TDBFMT = . 'YYYY MON DD HR:MN:SC.### (TDB) ::TDB' ) C C The meta-kernel: C CHARACTER*(*) METAKR PARAMETER ( METAKR = 'viewpr.tm' ) C C Maximum number of intervals in any window: C INTEGER MAXIVL PARAMETER ( MAXIVL = 1000 ) C C Maximum result window size: C INTEGER MAXWIN PARAMETER ( MAXWIN = 2 * MAXIVL ) C C SPICELIB cell bound: C INTEGER LBCELL PARAMETER ( LBCELL = -5 ) C C String length parameters: C INTEGER CORLEN PARAMETER ( CORLEN = 10 ) INTEGER FRNMLN PARAMETER ( FRNMLN = 32 ) INTEGER LNSIZE PARAMETER ( LNSIZE = 200 ) INTEGER NAMLEN PARAMETER ( NAMLEN = 32 ) INTEGER OPLEN PARAMETER ( OPLEN = 50 ) INTEGER TIMLEN PARAMETER ( TIMLEN = 50 ) C C Local variables C CHARACTER*(CORLEN) ABCORR CHARACTER*(NAMLEN) CRDSYS CHARACTER*(NAMLEN) COORD CHARACTER*(LNSIZE) LINE CHARACTER*(FRNMLN) OBSFRM CHARACTER*(OPLEN) RELATE CHARACTER*(NAMLEN) SRFPT CHARACTER*(TIMLEN) START CHARACTER*(TIMLEN) STOP CHARACTER*(NAMLEN) TARGET CHARACTER*(TIMLEN) TIMSTR CHARACTER*(LNSIZE) TITLE DOUBLE PRECISION ADJUST C C Confinement window used to store interval to be searched: C DOUBLE PRECISION CNFINE ( LBCELL : MAXWIN ) DOUBLE PRECISION ELVLIM DOUBLE PRECISION ETBEG DOUBLE PRECISION ETEND DOUBLE PRECISION INTBEG DOUBLE PRECISION INTEND DOUBLE PRECISION REVLIM C C STEPSZ is the step size, measured in seconds, used to search C for times bracketing a state transition. C DOUBLE PRECISION STEPSZ C C Result window used to store rise/set times: C DOUBLE PRECISION RISWIN ( LBCELL : MAXWIN ) C C Workspace array: C DOUBLE PRECISION WORK ( LBCELL : MAXWIN, NWMAX ) INTEGER I INTEGER WINSIZ C C Load the meta-kernel. C CALL FURNSH ( METAKR ) C C Assign the inputs for our search. C C Since we're interested in the apparent location of the C target, we use light time and stellar aberration C corrections. We use the "converged Newtonian" form C of the light time correction because this choice may C increase the accuracy of the occultation times we'll C compute using GFOCLT. C SRFPT = 'DSS-14' OBSFRM = 'DSS-14_TOPO' TARGET = 'MEX' ABCORR = 'CN+S' START = '2004 MAY 2 TDB' STOP = '2004 MAY 6 TDB' ELVLIM = 6.0D0 C C The elevation limit above has units of degrees; we convert C this value to radians for computation using SPICE routines. C We'll store the equivalent value in radians in REVLIM. C REVLIM = RPD() * ELVLIM C C Since SPICE doesn't directly support the AZ/EL coordinate C system, we use the equivalent constraint C C latitude > REVLIM C C in the latitudinal coordinate system, where the reference C frame is topocentric and is centered at the viewing location. C CRDSYS = 'LATITUDINAL' COORD = 'LATITUDE' RELATE = '>' C C The adjustment value only applies to absolute extrema C searches; simply give it an initial value of zero C for this inequality search. C ADJUST = 0.D0 C C STEPSZ is the step size, measured in seconds, used to search C for times bracketing a state transition. Since we don't expect C any events of interest to be shorter than five minutes, and C since the separation between events is well over 5 minutes, C we'll use this value as our step size. Units are seconds. C STEPSZ = 300.D0 C C Display a banner for the output report: C TITLE = 'Inputs for target visibility search:' CALL TOSTDO ( ' ' ) CALL TOSTDO ( TITLE ) CALL TOSTDO ( ' ' ) LINE = ' Target = #' CALL REPMC ( LINE, '#', TARGET, LINE ) CALL TOSTDO ( LINE ) LINE = ' Observation surface location = #' CALL REPMC ( LINE, '#', SRFPT, LINE ) CALL TOSTDO ( LINE ) LINE = ' Observer''s reference frame = #' CALL REPMC ( LINE, '#', OBSFRM, LINE ) CALL TOSTDO ( LINE ) LINE = ' Elevation limit (degrees) = #' CALL REPMF ( LINE, '#', ELVLIM, 7, 'F', LINE ) CALL TOSTDO ( LINE ) LINE = ' Aberration correction = #' CALL REPMC ( LINE, '#', ABCORR, LINE ) CALL TOSTDO ( LINE ) LINE = ' Step size (seconds) = #' CALL REPMF ( LINE, '#', STEPSZ, 9, 'F', LINE ) CALL TOSTDO ( LINE ) C C Convert the start and stop times to ET. C CALL STR2ET ( START, ETBEG ) CALL STR2ET ( STOP, ETEND ) C C Display the search interval start and stop times C using the format shown below. C C 2004 MAY 06 20:15:00.000 (TDB) C CALL TIMOUT ( ETBEG, TDBFMT, TIMSTR ) LINE = ' Start time = '//TIMSTR CALL TOSTDO ( LINE ) CALL TIMOUT ( ETEND, TDBFMT, TIMSTR ) LINE = ' Stop time = '//TIMSTR CALL TOSTDO ( LINE ) CALL TOSTDO ( ' ' ) C C Every SPICELIB window must have its size initialized. C C Initialize the "confinement" window with the interval C over which we'll conduct the search. C CALL SSIZED ( MAXWIN, CNFINE ) CALL WNINSD ( ETBEG, ETEND, CNFINE ) C C Initialize the result window; this window will contain C the rise/set times found by our search. C CALL SSIZED ( MAXWIN, RISWIN ) C C In the call below, the workspace dimensions are C C ( MAXWIN, NWMAX ) C C Now search for the time period, within our confinement C window, during which the apparent target has elevation C at least equal to the elevation limit. C CALL GFPOSC ( TARGET, OBSFRM, ABCORR, SRFPT, . CRDSYS, COORD, RELATE, REVLIM, . ADJUST, STEPSZ, CNFINE, MAXWIN, . NWMAX, WORK, RISWIN ) C C The function WNCARD returns the number of intervals C in a SPICE window. C WINSIZ = WNCARD( RISWIN ) IF ( WINSIZ .EQ. 0 ) THEN WRITE (*,*) 'No events were found.' ELSE C C Display the view periods. C LINE = 'Visibility times of # as seen from #:' CALL REPMC ( LINE, '#', TARGET, LINE ) CALL REPMC ( LINE, '#', SRFPT, LINE ) CALL TOSTDO ( LINE ) CALL TOSTDO ( ' ' ) DO I = 1, WINSIZ C C Fetch the start and stop times of the Ith interval C from the search result window RISWIN. C CALL WNFETD ( RISWIN, I, INTBEG, INTEND ) C C Convert the rise time to a TDB calendar string. C CALL TIMOUT ( INTBEG, TDBFMT, TIMSTR ) C C Write the string to standard output. C IF ( I .EQ. 1 ) THEN LINE = 'Visibility or window start time: #' ELSE LINE = 'Visibility start time: #' END IF CALL REPMC ( LINE, '#', TIMSTR, LINE ) CALL TOSTDO ( LINE ) C C Convert the set time to a TDB calendar string. C CALL TIMOUT ( INTEND, TDBFMT, TIMSTR ) C C Write the string to standard output. C IF ( I .EQ. WINSIZ ) THEN LINE = 'Visibility or window stop time: #' ELSE LINE = 'Visibility stop time: #' END IF CALL REPMC ( LINE, '#', TIMSTR, LINE ) CALL TOSTDO ( LINE ) CALL TOSTDO ( ' ' ) END DO END IF END Solution Sample Output
After compiling the program, execute it. The output is:
Inputs for target visibility search: Target = MEX Observation surface location = DSS-14 Observer's reference frame = DSS-14_TOPO Elevation limit (degrees) = 6.000000 Aberration correction = CN+S Step size (seconds) = 300.000000 Start time = 2004 MAY 02 00:00:00.000 (TDB) Stop time = 2004 MAY 06 00:00:00.000 (TDB) Visibility times of MEX as seen from DSS-14: Visibility or window start time: 2004 MAY 02 00:00:00.000 (TDB) Visibility stop time: 2004 MAY 02 05:35:03.096 (TDB) Visibility start time: 2004 MAY 02 16:09:14.078 (TDB) Visibility stop time: 2004 MAY 03 05:33:57.257 (TDB) Visibility start time: 2004 MAY 03 16:08:02.279 (TDB) Visibility stop time: 2004 MAY 04 05:32:50.765 (TDB) Visibility start time: 2004 MAY 04 16:06:51.259 (TDB) Visibility stop time: 2004 MAY 05 05:31:43.600 (TDB) Visibility start time: 2004 MAY 05 16:05:40.994 (TDB) Visibility or window stop time: 2004 MAY 06 00:00:00.000 (TDB) Find Times when Target is VisibleTask Statement
Compute the final results twice as well, using the results of both occultation searches. For each of the two shape model cases, store the set of time intervals when the spacecraft is visible in a SPICELIB window. We'll call this the ``result window.'' Display each of the intervals in each result window as a pair of start and stop times. Express each time as a TDB calendar date using the same format as in the previous program. Learning Goals
ApproachSolution steps
SolutionSolution Meta-Kernel
KPL/MK Example meta-kernel for geometric event finding hands-on coding lesson. Version 3.0.0 26-OCT-2017 (BVS) The names and contents of the kernels referenced by this meta-kernel are as follows: File Name Description ------------------------------ ------------------------------ de405xs.bsp Planetary ephemeris SPK, subsetted to cover only time range of interest. earthstns_itrf93_050714.bsp DSN station SPK. earth_topo_050714.tf DSN station frame definitions. earth_000101_060525_060303.bpc Binary PCK for Earth. naif0008.tls Generic LSK. ORMM__040501000000_00076XS.BSP MEX Orbiter trajectory SPK, subsetted to cover only time range of interest. pck00008.tpc Generic PCK. mars_lowres.bds Low-resolution Mars DSK. \begindata KERNELS_TO_LOAD = ( 'kernels/spk/de405xs.bsp' 'kernels/spk/earthstns_itrf93_050714.bsp' 'kernels/fk/earth_topo_050714.tf' 'kernels/pck/earth_000101_060525_060303.bpc' 'kernels/lsk/naif0008.tls' 'kernels/spk/ORMM__040501000000_00076XS.BSP' 'kernels/pck/pck00008.tpc' 'kernels/dsk/mars_lowres.bds' ) \begintext Solution Code
PROGRAM VISIBL IMPLICIT NONE C C Find and display the window of times when the MEX C spacecraft is above a specified elevation limit in the C topocentric reference frame of DSN station DSS-14 C and is not occulted by Mars. C C C SPICELIB functions C DOUBLE PRECISION RPD INTEGER WNCARD C C Global GF parameters: we import from this file C the definition of the GF workspace size parameter C C NWMAX C C and the occultation parameters C C OCCLN C SHPLEN C INCLUDE 'gf.inc' C C Local parameters C C Format string for time output: C CHARACTER*(*) TDBFMT PARAMETER ( TDBFMT = . 'YYYY MON DD HR:MN:SC.### TDB ::TDB' ) C C The meta-kernel: C CHARACTER*(*) METAKR PARAMETER ( METAKR = 'visibl.tm' ) C C Maximum number of events we can handle in our event set: C INTEGER MAXEVT PARAMETER ( MAXEVT = 1000 ) C C Maximum result window size: C INTEGER MAXWIN PARAMETER ( MAXWIN = 2 * MAXEVT ) C C SPICELIB cell bound: C INTEGER LBCELL PARAMETER ( LBCELL = -5 ) C C String length parameters: C INTEGER BDNMLN PARAMETER ( BDNMLN = 36 ) INTEGER CORLEN PARAMETER ( CORLEN = 10 ) INTEGER FRNMLN PARAMETER ( FRNMLN = 32 ) INTEGER LNSIZE PARAMETER ( LNSIZE = 78 ) INTEGER MTHLEN PARAMETER ( MTHLEN = 100 ) INTEGER NAMLEN PARAMETER ( NAMLEN = 32 ) INTEGER OPLEN PARAMETER ( OPLEN = 50 ) INTEGER TIMLEN PARAMETER ( TIMLEN = 28 ) C C Local variables C CHARACTER*(CORLEN) ABCORR CHARACTER*(BDNMLN) BACK CHARACTER*(FRNMLN) BFRAME CHARACTER*(MTHLEN) BSHAPE CHARACTER*(TIMLEN) BTMSTR CHARACTER*(NAMLEN) CRDSYS CHARACTER*(NAMLEN) COORD CHARACTER*(TIMLEN) ETMSTR CHARACTER*(FRNMLN) FFRAME CHARACTER*(FRNMLN) FRAME CHARACTER*(BDNMLN) FRONT CHARACTER*(MTHLEN) FSHAPE CHARACTER*(LNSIZE) LINE CHARACTER*(OCLLN) OCCTYP CHARACTER*(OPLEN) RELATE CHARACTER*(NAMLEN) SRFPT CHARACTER*(TIMLEN) START CHARACTER*(TIMLEN) STOP CHARACTER*(NAMLEN) TARGET CHARACTER*(LNSIZE) TITLE DOUBLE PRECISION ADJUST C C Confinement window used to store interval to be searched: C DOUBLE PRECISION CNFINE ( LBCELL : MAXEVT ) DOUBLE PRECISION DINTBG DOUBLE PRECISION DINTEN DOUBLE PRECISION ELVLIM DOUBLE PRECISION ETBEG DOUBLE PRECISION ETEND DOUBLE PRECISION INTBEG DOUBLE PRECISION INTEND DOUBLE PRECISION REVLIM C C STEPSZ is the step size, measured in seconds, used to search C for times bracketing a state transition. C DOUBLE PRECISION STEPSZ C C Result window used to store occultation times: C DOUBLE PRECISION OCCWIN ( LBCELL : MAXWIN ) C C Result window used to store occultation times C computed using DSK data: C DOUBLE PRECISION DOCWIN ( LBCELL : MAXWIN ) C C Result window used to store rise/set times: C DOUBLE PRECISION RISWIN ( LBCELL : MAXWIN ) C C Result windows used to store visibility periods: C DOUBLE PRECISION DVISWN ( LBCELL : MAXWIN ) DOUBLE PRECISION EVISWN ( LBCELL : MAXWIN ) C C Workspace array: C DOUBLE PRECISION WORK ( LBCELL : MAXWIN, NWMAX ) INTEGER I INTEGER WINSIZ C C Load the meta-kernel. C CALL FURNSH ( METAKR ) C C Assign the inputs for our search. C SRFPT = 'DSS-14' FRAME = 'DSS-14_TOPO' TARGET = 'MEX' ABCORR = 'CN+S' START = '2004 MAY 2 TDB' STOP = '2004 MAY 6 TDB' ELVLIM = 6.0D0 C C The elevation limit above has units of degrees; we convert C this value to radians for computation using SPICE routines. C We'll store the equivalent value in radians in REVLIM. C REVLIM = RPD() * ELVLIM C C Since we're interested in the apparent location of the C target, we use light time and stellar aberration C corrections. C C Since SPICE doesn't directly support the AZ/EL coordinate C system, we use the equivalent constraint C C latitude > REVLIM C C in the latitudinal coordinate system, where the reference C frame is topocentric and is centered at the viewing location. C CRDSYS = 'LATITUDINAL' COORD = 'LATITUDE' RELATE = '>' C C STEPSZ is the step size, measured in seconds, used to search C for times bracketing a state transition. Since we don't expect C any events of interest to be shorter than five minutes, and C since the separation between events is well over 5 minutes, C we'll use this value as our step size. Units are seconds. C STEPSZ = 300.D0 C C We model the target shape as a point. We either model the C blocking body's shape as an ellipsoid, or we represent its shap e C using actual topographic data. No body-fixed reference frame is C required for the target since its orientation is not used. C C We'll set the shape specifications just before our calls to C the GF occultation finding routine GFOCLT. C BACK = TARGET BSHAPE = 'POINT' BFRAME = ' ' FRONT = 'MARS' FFRAME = 'IAU_MARS' C C The occultation type should be set to 'ANY' for a point C target. C OCCTYP = 'ANY' C C Display a banner for the output report: C TITLE = 'Inputs for target visibility search:' CALL TOSTDO ( ' ' ) CALL TOSTDO ( TITLE ) CALL TOSTDO ( ' ' ) LINE = ' Target = #' CALL REPMC ( LINE, '#', TARGET, LINE ) CALL TOSTDO ( LINE ) LINE = ' Observation surface location = #' CALL REPMC ( LINE, '#', SRFPT, LINE ) CALL TOSTDO ( LINE ) LINE = ' Observer''s reference frame = #' CALL REPMC ( LINE, '#', FRAME, LINE ) CALL TOSTDO ( LINE ) LINE = ' Blocking body = #' CALL REPMC ( LINE, '#', FRONT, LINE ) CALL TOSTDO ( LINE ) LINE = ' Blocker''s reference frame = #' CALL REPMC ( LINE, '#', FFRAME, LINE ) CALL TOSTDO ( LINE ) LINE = ' Elevation limit (degrees) = #' CALL REPMF ( LINE, '#', ELVLIM, 7, 'F', LINE ) CALL TOSTDO ( LINE ) LINE = ' Aberration correction = #' CALL REPMC ( LINE, '#', ABCORR, LINE ) CALL TOSTDO ( LINE ) LINE = ' Step size (seconds) = #' CALL REPMF ( LINE, '#', STEPSZ, 9, 'F', LINE ) CALL TOSTDO ( LINE ) C C Convert the start and stop times to ET. C CALL STR2ET ( START, ETBEG ) CALL STR2ET ( STOP, ETEND ) C C Display the search interval start and stop times C using the format shown below. C C 2004 MAY 06 20:15:00.000 (TDB) C CALL TIMOUT ( ETBEG, TDBFMT, BTMSTR ) LINE = ' Start time = '//BTMSTR CALL TOSTDO ( LINE ) CALL TIMOUT ( ETEND, TDBFMT, ETMSTR ) LINE = ' Stop time = '//ETMSTR CALL TOSTDO ( LINE ) CALL TOSTDO ( ' ' ) C C Every SPICELIB window must have its size initialized. C C Initialize the "confinement" window with the interval C over which we'll conduct the search. C CALL SSIZED ( MAXWIN, CNFINE ) CALL WNINSD ( ETBEG, ETEND, CNFINE ) C C Initialize the result window; this window will contain C the rise/set times found by our search. C CALL SSIZED ( MAXWIN, RISWIN ) C C Initialize the occultation and visibility windows. C CALL SSIZED ( MAXWIN, OCCWIN ) CALL SSIZED ( MAXWIN, DOCWIN ) CALL SSIZED ( MAXWIN, EVISWN ) CALL SSIZED ( MAXWIN, DVISWN ) C C The adjustment value only applies to absolute extrema C searches; simply give it an initial value of zero C for this inequality search. C ADJUST = 0.D0 C C Note that the workspace dimensions are ( MAXWIN, NWMAX ). C C Now search for the time period, within our confinement C window, during which the apparent target has elevation C at least equal to the elevation limit. C CALL GFPOSC ( TARGET, FRAME, ABCORR, SRFPT, . CRDSYS, COORD, RELATE, REVLIM, . ADJUST, STEPSZ, CNFINE, MAXWIN, . NWMAX, WORK, RISWIN ) C C Now find the times when the apparent target is above C the elevation limit and is not occulted by the C blocking body (Mars). We'll find the times when the target C is above the elevation limit and *is* occulted, then subtract C that window from the view period window RISWIN found above. C C For this occultation search, we can use RISWIN as C the confinement window because we're not interested in C occultations that occur when the target is below the C elevation limit. C C Find occultations within the view period window. C FSHAPE = 'ELLIPSOID' WRITE (*,*) 'Searching using ellipsoid target shape model...' CALL GFOCLT ( OCCTYP, FRONT, FSHAPE, FFRAME, . BACK, BSHAPE, BFRAME, ABCORR, . SRFPT, STEPSZ, RISWIN, OCCWIN ) WRITE (*,*) 'Done.' C C Subtract the occultation window from the view period C window: this yields the time periods when the target C is visible. C CALL WNDIFD ( RISWIN, OCCWIN, EVISWN ) C C Repeat the search using low-resolution DSK data C for the front body. C FSHAPE = 'DSK/UNPRIORITIZED' WRITE (*,*) 'Searching using DSK target shape model...' CALL GFOCLT ( OCCTYP, FRONT, FSHAPE, FFRAME, . BACK, BSHAPE, BFRAME, ABCORR, . SRFPT, STEPSZ, RISWIN, DOCWIN ) WRITE (*,*) 'Done.' CALL WNDIFD ( RISWIN, DOCWIN, DVISWN ) C C The function WNCARD returns the number of intervals C in a SPICE window. C WINSIZ = WNCARD( EVISWN ) IF ( WINSIZ .EQ. 0 ) THEN WRITE (*,*) 'No events were found.' ELSE C C Display the visibility time periods. C WRITE (*,*) ' ' LINE = 'Visibility start and stop times of ' . // '# as seen from #' CALL REPMC ( LINE, '#', TARGET, LINE ) CALL REPMC ( LINE, '#', SRFPT, LINE ) WRITE (*, '(A)') LINE WRITE (*, '(A)') 'using both ellipsoidal and DSK ' . // 'target shape models:' WRITE (*,*) ' ' DO I = 1, WINSIZ C C Fetch the start and stop times of the Ith interval C from the ellipsoid search result window EVISWN. C CALL WNFETD ( EVISWN, I, INTBEG, INTEND ) C C Convert the start and stop times to TDB calendar C strings. Write the results. C CALL TIMOUT ( INTBEG, TDBFMT, BTMSTR ) CALL TIMOUT ( INTEND, TDBFMT, ETMSTR ) WRITE (*,'('' Ell: '',A, '' : '', A)' ) BTMSTR, ETMSTR C C Fetch the start and stop times of the Ith interval C from the DSK search result window DVISWN. C CALL WNFETD ( DVISWN, I, DINTBG, DINTEN ) C C Convert the start and stop times to TDB calendar C strings. Write the results. C CALL TIMOUT ( DINTBG, TDBFMT, BTMSTR ) CALL TIMOUT ( DINTEN, TDBFMT, ETMSTR ) WRITE (*,'('' DSK: '',A, '' : '', A)' ) BTMSTR, ETMSTR WRITE (*,*) ' ' END DO END IF END Solution Sample Output
After compiling the program, execute it. The output is:
Inputs for target visibility search: Target = MEX Observation surface location = DSS-14 Observer's reference frame = DSS-14_TOPO Blocking body = MARS Blocker's reference frame = IAU_MARS Elevation limit (degrees) = 6.000000 Aberration correction = CN+S Step size (seconds) = 300.000000 Start time = 2004 MAY 02 00:00:00.000 TDB Stop time = 2004 MAY 06 00:00:00.000 TDB Searching using ellipsoid target shape model... Done. Searching using DSK target shape model... Done. Visibility start and stop times of MEX as seen from DSS-14 using both ellipsoidal and DSK target shape models: Ell: 2004 MAY 02 00:00:00.000 TDB : 2004 MAY 02 04:49:30.827 TDB DSK: 2004 MAY 02 00:00:00.000 TDB : 2004 MAY 02 04:49:32.645 TDB Ell: 2004 MAY 02 16:09:14.078 TDB : 2004 MAY 02 20:00:22.514 TDB DSK: 2004 MAY 02 16:09:14.078 TDB : 2004 MAY 02 20:00:23.980 TDB Ell: 2004 MAY 02 21:01:38.222 TDB : 2004 MAY 03 03:35:42.256 TDB DSK: 2004 MAY 02 21:01:43.206 TDB : 2004 MAY 03 03:35:44.140 TDB Ell: 2004 MAY 03 04:36:42.484 TDB : 2004 MAY 03 05:33:57.257 TDB DSK: 2004 MAY 03 04:36:46.868 TDB : 2004 MAY 03 05:33:57.257 TDB Ell: 2004 MAY 03 16:08:02.279 TDB : 2004 MAY 03 18:46:26.013 TDB DSK: 2004 MAY 03 16:08:02.279 TDB : 2004 MAY 03 18:46:27.306 TDB Ell: 2004 MAY 03 19:46:54.618 TDB : 2004 MAY 04 02:21:44.562 TDB DSK: 2004 MAY 03 19:46:59.734 TDB : 2004 MAY 04 02:21:46.574 TDB Ell: 2004 MAY 04 03:21:56.347 TDB : 2004 MAY 04 05:32:50.765 TDB DSK: 2004 MAY 04 03:22:00.862 TDB : 2004 MAY 04 05:32:50.765 TDB Ell: 2004 MAY 04 16:06:51.259 TDB : 2004 MAY 04 17:32:25.809 TDB DSK: 2004 MAY 04 16:06:51.259 TDB : 2004 MAY 04 17:32:27.118 TDB Ell: 2004 MAY 04 18:32:05.975 TDB : 2004 MAY 05 01:07:48.264 TDB DSK: 2004 MAY 04 18:32:11.057 TDB : 2004 MAY 05 01:07:50.061 TDB Ell: 2004 MAY 05 02:07:11.601 TDB : 2004 MAY 05 05:31:43.600 TDB DSK: 2004 MAY 05 02:07:16.253 TDB : 2004 MAY 05 05:31:43.600 TDB Ell: 2004 MAY 05 16:05:40.994 TDB : 2004 MAY 05 16:18:35.560 TDB DSK: 2004 MAY 05 16:05:40.994 TDB : 2004 MAY 05 16:18:36.994 TDB Ell: 2004 MAY 05 17:17:27.717 TDB : 2004 MAY 05 23:54:04.672 TDB DSK: 2004 MAY 05 17:17:32.385 TDB : 2004 MAY 05 23:54:06.221 TDB Extra Credit
These ``extra credit'' tasks are provided as task statements, and unlike the regular tasks, no approach or solution source code is provided. In the next section, you will find the numeric solutions to the questions asked in these tasks. Task statements
2004 MAY 2 TDB 2004 MAY 6 TDB
2004 MAY 2 TDB 2004 MAY 6 TDB
2004 MAY 2 TDB 2004 MAY 6 TDB
Solutions
Inputs for equator crossing search: Target = MEX Observer = MARS Observer's reference frame = IAU_MARS Latitude limit (degrees) = 0.000000 Aberration correction = NONE Step size (seconds) = 300.000000 Start time = 2004 MAY 02 00:00:00.000 (TDB) Stop time = 2004 MAY 06 00:00:00.000 (TDB) MEX MARS equator crossing times: Equator crossing or start time: 2004 MAY 02 05:00:08.334 (TDB) Equator crossing time: 2004 MAY 02 06:15:13.074 (TDB) Equator crossing time: 2004 MAY 02 12:35:14.856 (TDB) Equator crossing time: 2004 MAY 02 13:50:09.161 (TDB) Equator crossing time: 2004 MAY 02 20:10:24.439 (TDB) Equator crossing time: 2004 MAY 02 21:25:10.344 (TDB) Equator crossing time: 2004 MAY 03 03:45:26.758 (TDB) Equator crossing time: 2004 MAY 03 05:00:04.086 (TDB) Equator crossing time: 2004 MAY 03 11:20:32.419 (TDB) Equator crossing time: 2004 MAY 03 12:34:57.968 (TDB) Equator crossing time: 2004 MAY 03 18:55:34.883 (TDB) Equator crossing time: 2004 MAY 03 20:09:53.063 (TDB) Equator crossing time: 2004 MAY 04 02:30:35.509 (TDB) Equator crossing time: 2004 MAY 04 03:44:42.753 (TDB) Equator crossing time: 2004 MAY 04 10:05:41.638 (TDB) Equator crossing time: 2004 MAY 04 11:19:38.397 (TDB) Equator crossing time: 2004 MAY 04 17:40:41.405 (TDB) Equator crossing time: 2004 MAY 04 18:54:31.413 (TDB) Equator crossing time: 2004 MAY 05 01:15:45.967 (TDB) Equator crossing time: 2004 MAY 05 02:29:25.294 (TDB) Equator crossing time: 2004 MAY 05 08:50:53.931 (TDB) Equator crossing time: 2004 MAY 05 10:04:26.915 (TDB) Equator crossing time: 2004 MAY 05 16:25:58.350 (TDB) Equator crossing or stop time: 2004 MAY 05 17:39:23.889 (TDB)
Inputs for periapsis search: Target = MEX Observer = MARS Aberration correction = NONE Step size (seconds) = 300.000000 Start time = 2004 MAY 02 00:00:00.000 (TDB) Stop time = 2004 MAY 06 00:00:00.000 (TDB) MEX periapsis times: Periapsis or start time: 2004 MAY 02 05:57:51.000 (TDB) Periapsis time: 2004 MAY 02 13:32:43.325 (TDB) Periapsis time: 2004 MAY 02 21:07:41.124 (TDB) Periapsis time: 2004 MAY 03 04:42:30.648 (TDB) Periapsis time: 2004 MAY 03 12:17:21.143 (TDB) Periapsis time: 2004 MAY 03 19:52:12.267 (TDB) Periapsis time: 2004 MAY 04 03:26:57.755 (TDB) Periapsis time: 2004 MAY 04 11:01:49.826 (TDB) Periapsis time: 2004 MAY 04 18:36:38.448 (TDB) Periapsis time: 2004 MAY 05 02:11:28.558 (TDB) Periapsis time: 2004 MAY 05 09:46:26.309 (TDB) Periapsis or end time: 2004 MAY 05 17:21:18.875 (TDB)
Inputs for apoapsis search: Target = MEX Observer = MARS Aberration correction = NONE Step size (seconds) = 300.000000 Start time = 2004 MAY 02 00:00:00.000 (TDB) Stop time = 2004 MAY 06 00:00:00.000 (TDB) MEX apoapsis times: Apoapsis or start time: 2004 MAY 02 02:10:24.948 (TDB) Apoapsis time: 2004 MAY 02 09:45:19.189 (TDB) Apoapsis time: 2004 MAY 02 17:20:14.194 (TDB) Apoapsis time: 2004 MAY 03 00:55:07.633 (TDB) Apoapsis time: 2004 MAY 03 08:29:57.890 (TDB) Apoapsis time: 2004 MAY 03 16:04:48.524 (TDB) Apoapsis time: 2004 MAY 03 23:39:36.745 (TDB) Apoapsis time: 2004 MAY 04 07:14:25.662 (TDB) Apoapsis time: 2004 MAY 04 14:49:15.904 (TDB) Apoapsis time: 2004 MAY 04 22:24:05.351 (TDB) Apoapsis time: 2004 MAY 05 05:58:59.270 (TDB) Apoapsis time: 2004 MAY 05 13:33:54.433 (TDB) Apoapsis or stop time: 2004 MAY 05 21:08:50.211 (TDB) |