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I/O
Examples
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Abstract


   CSPICE_SPKCVT returns the state, relative to a specified observer, of a
   target having constant velocity in a specified reference frame. The
   target's state is provided by the calling program rather than by
   loaded SPK files.

I/O


   Given:

      trgsta   geometric state of a target moving at constant velocity
               relative to its center of motion 'trgctr', expressed in
               the reference frame 'trgref', at the epoch 'trgepc'.

               'trgsta' is a six-dimensional vector representing
               position and velocity in Cartesian coordinates: the
               first three components represent the position of a
               target relative to its center of motion; the last three
               components represent the velocity of the target.

               Units are always km and km/sec.

               [6,1] = size(trgsta), double = class(trgsta)

      trgepc   epoch, expressed as seconds past J2000 TDB, at which the
               target state 'trgsta' is applicable. For other epochs, the
               position of the target relative to its center of motion is
               linearly extrapolated from the position at 'trgepc' using
               the velocity component of 'trgsta'.

               'trgepc' is independent of the epoch 'et' at which the
               state of the target relative to the observer is to be
               computed.

               [1,1] = size(trgepc), double = class(trgepc)

      trgctr   name of the center of motion of 'trgsta'. The
               ephemeris of 'trgctr' is provided by loaded SPK files.

               Optionally, you may supply the integer ID code for
               the object as an integer string. For example both
               'MOON' and '301' are legitimate strings that indicate
               the moon is the center of motion.

               Case and leading and trailing blanks are not
               significant in the string 'trgctr'.

               [1,c1] = size(trgctr), char = class(trgctr)

                  or

               [1,1] = size(trgctr); cell = class(trgctr)

      trgref   name of the reference frame relative to which
               the input state 'trgsta' is expressed. The target has
               constant velocity relative to its center of motion
               in this reference frame.

               Case and leading and trailing blanks are not
               significant in the string 'trgref'.

               [1,c2] = size(trgref), char = class(trgref)

                  or

               [1,1] = size(trgref); cell = class(trgref)

      et       ephemeris time at which the state of the
               target relative to the observer is to be computed. 'et' is
               expressed as seconds past J2000 TDB. 'et' refers to time
               at the observer's location.

               'et' is independent of the target epoch 'trgepc'.

               [1,1] = size(et), double = class(et)

      outref   name of the reference frame with respect to which
               the output state is expressed.

               When 'outref' is time-dependent (non-inertial), its
               orientation relative to the J2000 frame is evaluated in
               the manner commanded by the input argument 'refloc' (see
               description below).

               Case and leading and trailing blanks are not significant
               in the string 'outref'.

               [1,c3] = size(outref), char = class(outref)

                  or

               [1,1] = size(outref); cell = class(outref)

      refloc   name indicating the output reference frame
               evaluation locus: this is the location associated
               with the epoch at which this routine is to evaluate
               the orientation, relative to the J2000 frame, of the
               output frame 'outref'. The values and meanings of
               'refloc' are:

                  'OBSERVER'  Evaluate 'outref' at the observer's
                              epoch 'et'.

                              Normally the locus 'OBSERVER' should
                              be selected when 'outref' is centered
                              at the observer.


                  'TARGET'    Evaluate 'outref' at the target epoch;
                              letting 'ltime' be the one-way light time
                              between the target and observer, the
                              target epoch is

                                 et-ltime  if reception aberration
                                           corrections are used

                                 et+ltime  if transmission aberration
                                           corrections are used

                                 et        if no aberration corrections
                                           are used

                              Normally the locus 'TARGET' should
                              be selected when 'outref' is 'trgref',
                              the frame in which the target state
                              is specified.


                  'CENTER'    Evaluate the frame 'outref' at the epoch
                              associated its center. This epoch,
                              which we'll call 'etctr', is determined
                              as follows:

                                 Let 'ltctr' be the one-way light time
                                 between the observer and the center
                                 of 'outref'. Then 'etctr' is

                                    et-ltctr  if reception
                                              aberration corrections
                                              are used

                                    et+ltctr  if transmission
                                              aberration corrections
                                              are used

                                    et        if no aberration
                                              corrections are used


                              The locus 'CENTER' should be selected
                              when the user intends to obtain
                              results compatible with those produced
                              by cspice_spkezr.

               When 'outref' is inertial, all choices of 'refloc'
               yield the same results.

               Case and leading and trailing blanks are not
               significant in the string 'refloc'.

               [1,c4] = size(refloc), char = class(refloc)

                  or

               [1,1] = size(refloc); cell = class(refloc)

      abcorr   name indicating the aberration corrections to be
               applied to the observer-target state to account for one-way
               light time and stellar aberration.

               'abcorr' may be any of the following:

                  'NONE'     Apply no correction. Return the
                             geometric state of the target
                             relative to the observer.

               The following values of 'abcorr' apply to the
               'reception' case in which photons depart from the
               target's location at the light-time corrected epoch
               et-ltime and *arrive* at the observer's location at 'et':

                  'LT'       Correct for one-way light time (also
                             called "planetary aberration") using a
                             Newtonian formulation. This correction
                             yields the state of the target at the
                             moment it emitted photons arriving at
                             the observer at 'et'.

                             The light time correction uses an
                             iterative solution of the light time
                             equation. The solution invoked by the
                             'LT' option uses one iteration.

                  'LT+S'     Correct for one-way light time and
                             stellar aberration using a Newtonian
                             formulation. This option modifies the
                             state obtained with the 'LT' option to
                             account for the observer's velocity
                             relative to the solar system
                             barycenter. The result is the apparent
                             state of the target---the position and
                             velocity of the target as seen by the
                             observer.

                  'CN'       Converged Newtonian light time
                             correction. In solving the light time
                             equation, the 'CN' correction iterates
                             until the solution converges.

                  'CN+S'     Converged Newtonian light time
                             and stellar aberration corrections.


               The following values of 'abcorr' apply to the
               "transmission" case in which photons *depart* from
               the observer's location at 'et' and arrive at the
               target's location at the light-time corrected epoch
               et+ltime:

                  'XLT'      "Transmission" case:  correct for
                             one-way light time using a Newtonian
                             formulation. This correction yields the
                             state of the target at the moment it
                             receives photons emitted from the
                             observer's location at 'et'.

                  'XLT+S'    "Transmission" case:  correct for
                             one-way light time and stellar
                             aberration using a Newtonian
                             formulation  This option modifies the
                             state obtained with the 'XLT' option to
                             account for the observer's velocity
                             relative to the solar system
                             barycenter. The position component of
                             the computed target state indicates the
                             direction that photons emitted from the
                             observer's location must be "aimed" to
                             hit the target.

                  'XCN'      "Transmission" case:  converged
                             Newtonian light time correction.

                  'XCN+S'    "Transmission" case:  converged
                             Newtonian light time and stellar
                             aberration corrections.

               Neither special nor general relativistic effects are
               accounted for in the aberration corrections applied
               by this routine.

               Case and leading and trailing blanks are not
               significant in the string 'abcorr'.

               [1,c5] = size(abcorr), char = class(abcorr)

                  or

               [1,1] = size(abcorr); cell = class(abcorr)

      obsrvr   name of an observing body. Optionally, you
               may supply the ID code of the object as an integer
               string. For example, both 'EARTH' and '399' are
               legitimate strings to supply to indicate the
               observer is Earth.

               Case and leading and trailing blanks are not
               significant in the string 'obsrvr'.

               [1,c6] = size(obsrvr), char = class(obsrvr)

                  or

               [1,1] = size(obsrvr); cell = class(obsrvr)

   the call:

      [state, lt] = cspice_spkcvt( trgsta, trgepc, trgctr, ...
                                   trgref, et,     outref, ...
                                   evlref, abcorr, obsrvr )

   returns:

      state   state of the target relative to the specified
              observer. 'state' is corrected for the specified
              aberrations and is expressed with respect to the
              reference frame specified by 'outref'. The first three
              components of 'state' represent the x-, y- and
              z-components of the target's position; the last three
              components form the corresponding velocity vector.

              The position component of 'state' points from the
              observer's location at 'et' to the aberration-corrected
              location of the target. Note that the sense of the
              position vector is independent of the direction of
              radiation travel implied by the aberration
              correction.

              The velocity component of 'state' is the derivative
              with respect to time of the position component of
              'state'.

              Units are always km and km/sec.

              When 'state' is expressed in a time-dependent
              (non-inertial) output frame, the orientation of that
              frame relative to the J2000 frame is evaluated in the
              manner indicated by the input argument 'refloc' (see
              description above).

              [6,1] = size(state), double = class(state)

      lt      one-way light time between the observer
              and target in seconds. If the target state is corrected
              for aberrations, then 'ltime' is the one-way light time
              between the observer and the light time corrected
              target location.

              [1,1] = size(lt), double = class(lt)

Examples


   Any 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.

      Use the meta-kernel shown below to load the required SPICE
      kernels.


      KPL/MK

         File name: spkcvt.tm

         This is the meta-kernel file for the header code example for
         the subroutine cspice_spkcvo. These kernel files can be found on
         the NAIF website.

         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
            ---------                        --------
            de421.bsp                        Planetary ephemeris
            pck00010.tpc                     Planet orientation and
                                             radii
            naif0010.tls                     Leapseconds
            earth_720101_070426.bpc          Earth historical
                                             binary PCK
            earthstns_itrf93_050714.bsp      DSN station SPK
            earth_topo_050714.tf             DSN station FK
            mgs_moc_v20.ti                   MGS MOC instrument
                                             parameters
            mgs_sclkscet_00061.tsc           MGS SCLK coefficients
            mgs_sc_ext12.bc                  MGS s/c bus attitude
            mgs_ext12_ipng_mgs95j.bsp        MGS ephemeris

         \begindata

         KERNELS_TO_LOAD = ( 'de421.bsp',
                             'pck00010.tpc',
                             'naif0010.tls',
                             'earth_720101_070426.bpc',
                             'earthstns_itrf93_050714.bsp',
                             'earth_topo_050714.tf',
                             'mgs_moc_v20.ti',
                             'mgs_sclkscet_00061.tsc',
                             'mgs_sc_ext12.bc',
                             'mgs_ext12_ipng_mgs95j.bsp'  )

         \begintext

   Example:

      %
      % Program spkcvt_ex1
      %
      %
      % This program demonstrates the use of cspice_spkcvt.
      % Computations are performed using all three possible
      % values of the output frame evaluation locus `refloc':
      %
      % 'TARGET'
      % 'OBSERVER'
      % 'CENTER'
      %
      % Several unrelated computations are performed in this
      % program. In particular, computations involving a surface
      % point on Mars are included simply to demonstrate use of
      % the 'OBSERVER' option.

      %
      % Local constants
      %

      CAMERA =  'MGS_MOC_NA';
      MAXBND =  100;
      META   =  'spkcvt.tm';
      TIMFMT =  'YYYY MON DD HR:MN:SC.###### UTC';
      TIMFM2 =  'YYYY MON DD HR:MN:SC.###### TDB ::TDB';

      %
      % Load SPICE kernels.
      %
      cspice_furnsh( META )

      %
      % Convert the observation time to seconds past J2000 TDB.
      %
      obstim = '2003 OCT 13 06:00:00.000000 UTC';

      et = cspice_str2et( obstim );

      %
      % Set the observer, target center, and target frame.
      %
      obsrvr = 'MGS';
      trgctr = 'EARTH';
      trgref = 'ITRF93';

      %
      % Set the state of DSS-14 relative to the earth's
      % center at the J2000 epoch, expressed in the
      % ITRF93 reference frame. Values come from the
      % earth station SPK specified in the meta-kernel.
      %
      % The velocity is non-zero due to tectonic
      % plate motion.

      trgepc =  0.0;

      trgsta = [ -2353.6213656676991, -4641.3414911499403,  ...
                 3677.0523293197439,  -0.00000000000057086, ...
                 0.00000000000020549, -0.00000000000012171 ]';

      %
      % Find the apparent state of the station relative
      % to the spacecraft in the ITRF93 reference frame.
      % Evaluate the earth's orientation, that is the
      % orientation of the ITRF93 frame relative to the
      % J2000 frame, at the epoch obtained by correcting
      % the observation time for one-way light time. This
      % correction is obtained by setting `refloc' to 'TARGET'.
      %
      outref = 'ITRF93';
      abcorr = 'CN+S';

      refloc = 'TARGET';

      %
      % Compute the observer-target state.
      %
      [state0, lt0] = cspice_spkcvt( trgsta, trgepc, trgctr, trgref, ...
                                     et,     outref, refloc, abcorr, ...
                                     obsrvr );

      %
      % Display the computed state and light time.
      %
      emitim = cspice_timout( et-lt0, TIMFMT );
      trgtim = cspice_timout( trgepc, TIMFM2 );

      fprintf( ' Frame evaluation locus:   %s\n\n', refloc )

      fprintf( ' Observer:                 %s\n', obsrvr )
      fprintf( ' Observation time:         %s\n', obstim )
      fprintf( ' Target center:            %s\n', trgctr )
      fprintf( ' Target-center state time: %s\n', trgtim )
      fprintf( ' Target frame:             %s\n', trgref )
      fprintf( ' Emission time:            %s\n', emitim )
      fprintf( ' Output reference frame:   %s\n', outref )
      fprintf( ' Aberration correction:    %s\n\n', abcorr )

      fprintf( ' Observer-target position (km):\n' )
      fprintf( '%20.8f %20.8f %20.8f\n', state0(1:3) )
      fprintf( ' Observer-target velocity (km/s):\n' )
      fprintf( '%20.8f %20.8f %20.8f\n', state0(4:6) )
      fprintf( ' Light time (s):        %20.8f\n\n', lt0 )

      %
      % Repeat the computation, this time evaluating the
      % earth's orientation at the epoch obtained by
      % subtracting from the observation time the one way
      % light time from the earth's center.
      %
      % This is equivalent to looking up the observer-target
      % state using cspice_spkezr.
      %
      refloc = 'CENTER';

      [state1, lt1] = cspice_spkcvt( trgsta, trgepc, trgctr, trgref, ...
                                     et,     outref, refloc, abcorr, ...
                                    obsrvr );

      %
      % Display the computed state and light time.
      %
      emitim = cspice_timout( et-lt1, TIMFMT );

      fprintf( '  Frame evaluation locus:   %s\n\n', refloc )

      fprintf( ' Observer:                 %s\n', obsrvr )
      fprintf( ' Observation time:         %s\n', obstim )
      fprintf( ' Target center:            %s\n', trgctr )
      fprintf( ' Target-center state time: %s\n', trgtim )
      fprintf( ' Target frame:             %s\n', trgref )
      fprintf( ' Emission time:            %s\n', emitim )
      fprintf( ' Output reference frame:   %s\n', outref )
      fprintf( ' Aberration correction:    %s\n', abcorr )

      fprintf( ' Observer-target position (km):\n' )
      fprintf( '%20.8f %20.8f %20.8f\n', state1(1:3) )
      fprintf( ' Observer-target velocity (km/s):\n' )
      fprintf( '%20.8f %20.8f %20.8f\n', state1(4:6) )
      fprintf( ' Light time (s):        %20.8f\n\n', lt1 )

      fprintf( ' Distance between above positions (km): %20.8f\n', ...
                         cspice_vdist( state0(1:3), state1(1:3) ) )
      fprintf( ' Velocity difference magnitude  (km/s): %20.8f\n\n', ...
                         cspice_vdist( state0(4:6), state1(4:6) ) )

      %
      % Check: compare the state computed directly above
      % to one produced by cspice_spkezr:
      %
      target = 'DSS-14';

      [state2, lt2] = cspice_spkezr( target,  et, outref,  abcorr, ...
                                     obsrvr );

      fprintf( ' State computed using cspice_spkezr:\n\n' )

      fprintf( ' Observer:               %s\n', obsrvr )
      fprintf( ' Observation time:       %s\n', obstim )
      fprintf( ' Target:                 %s\n', target )
      fprintf( ' Output reference frame: %s\n', outref )
      fprintf( ' Aberration correction:  %s\n\n', abcorr )

      fprintf( ' Observer-target position (km):\n' )
      fprintf( '%20.8f %20.8f %20.8f\n', state2(1:3) )
      fprintf( ' Observer-target velocity (km/s):\n' )
      fprintf( '%20.8f %20.8f %20.8f\n', state2(4:6) )
      fprintf( ' Light time (s):        %20.8f\n\n', lt2 )

      fprintf( ' Distance between last two positions (km): %20.8f\n', ...
                         cspice_vdist( state1(1:3), state2(1:3) ) )
      fprintf( ' Velocity difference magnitude  (km/s): %20.8f\n\n', ...
                         cspice_vdist( state1(4:6), state2(4:6) ) )

      %
      % Finally, compute an observer-target state in
      % a frame centered at the observer.
      % The reference frame will be that of the
      % MGS MOC NA camera.
      %
      % In this case we'll use as the target the surface
      % intercept on Mars of the camera boresight. This
      % allows us to easily verify the correctness of
      % the results returned by cspice_spkcvt.
      %
      % Get camera frame and FOV parameters. We'll need
      % the camera ID code first.
      %
      [camid, found] = cspice_bodn2c( CAMERA );

      if ( ~found )
         error( 'Camera name could not be mapped to an ID code.' )
      end

      %
      % cspice_getfov will return the name of the camera-fixed frame
      % in the string `camref', the camera boresight vector in
      % the array `bsight', and the FOV corner vectors in the
      % array `bounds'. All we're going to use are the camera
      % frame name and camera boresight.
      %

      [shape, camref, bsight, bounds] = cspice_getfov( camid, MAXBND );

      %
      % Find the camera boresight surface intercept.
      %

      trgctr = 'MARS';
      trgref = 'IAU_MARS';

      [spoint, trgep2, srfvec, found] = cspice_sincpt( ...
                               'Ellipsoid', trgctr,    ...
                               et,     trgref, abcorr, ...
                               obsrvr, camref, bsight );

      %
      % Set the position component of the state vector
      % `trgst2' to `spoint'.
      %
      % Set the velocity of the target state to zero.
      %
      % Since the velocity is zero, we can pick any value
      % as the target epoch we choose 0 seconds past
      % J2000 TDB.
      %
      trgst2 = [ spoint; [ 0., 0., 0. ]' ];

      trgepc = 0.;
      outref = camref;

      refloc = 'OBSERVER';

      [state3, lt3] = cspice_spkcvt( trgst2, trgepc, trgctr, trgref, ...
                                     et,     outref, refloc, abcorr, ...
                                     obsrvr );

      %
      % Convert the emission time and the target state
      % evaluation epoch to strings for output.
      %
      emitim = cspice_timout( et-lt3, TIMFMT );
      trgtim = cspice_timout( trgepc, TIMFM2 );

      %
      % Convert the emission time and the target state
      % evaluation epoch to strings for output.
      %
      emitim = cspice_timout( et-lt3, TIMFMT );

      fprintf( ' Frame evaluation locus:   %s\n\n', refloc )

      fprintf( ' Observer:                 %s\n', obsrvr )
      fprintf( ' Observation time:         %s\n', obstim )
      fprintf( ' Target center:            %s\n', trgctr )
      fprintf( ' Target-center state time: %s\n', trgtim )
      fprintf( ' Target frame:             %s\n', trgref )
      fprintf( ' Emission time:            %s\n', emitim )
      fprintf( ' Output reference frame:   %s\n', outref )
      fprintf( ' Aberration correction:    %s\n', abcorr )

      fprintf( ' Observer-target position (km):\n' )
      fprintf( '%20.8f %20.8f %20.8f\n', state3(1:3) )
      fprintf( ' Observer-target velocity (km/s):\n' )
      fprintf( '%20.8f %20.8f %20.8f\n', state3(4:6) )
      fprintf( ' Light time (s):        %20.8f\n', lt3 )

      fprintf( ' Target range from cspice_sincpt (km): %20.8f\n', ...
                                         cspice_vnorm( srfvec ) )

      %
      % It's always good form to unload kernels after use,
      % particularly in Matlab due to data persistence.
      %
      cspice_kclear

   MATLAB outputs:

      Frame evaluation locus:   TARGET

      Observer:                 MGS
      Observation time:         2003 OCT 13 06:00:00.000000 UTC
      Target center:            EARTH
      Target-center state time: 2000 JAN 01 12:00:00.000000 TDB
      Target frame:             ITRF93
      Emission time:            2003 OCT 13 05:55:44.232914 UTC
      Output reference frame:   ITRF93
      Aberration correction:    CN+S

      Observer-target position (km):
        52746468.84236781    52367725.79656220    18836142.68955782
      Observer-target velocity (km/s):
            3823.39593314       -3840.60002121           2.21337692
      Light time (s):                255.76708533

       Frame evaluation locus:   CENTER

      Observer:                 MGS
      Observation time:         2003 OCT 13 06:00:00.000000 UTC
      Target center:            EARTH
      Target-center state time: 2000 JAN 01 12:00:00.000000 TDB
      Target frame:             ITRF93
      Emission time:            2003 OCT 13 05:55:44.232914 UTC
      Output reference frame:   ITRF93
      Aberration correction:    CN+S
      Observer-target position (km):
        52746419.34641990    52367775.65039122    18836142.68968301
      Observer-target velocity (km/s):
            3823.40103499       -3840.59789000           2.21337692
      Light time (s):                255.76708533

      Distance between above positions (km):          70.25135676
      Velocity difference magnitude  (km/s):           0.00552910

      State computed using cspice_spkezr:

      Observer:               MGS
      Observation time:       2003 OCT 13 06:00:00.000000 UTC
      Target:                 DSS-14
      Output reference frame: ITRF93
      Aberration correction:  CN+S

      Observer-target position (km):
        52746419.34641990    52367775.65039122    18836142.68968301
      Observer-target velocity (km/s):
            3823.40103499       -3840.59789000           2.21337692
      Light time (s):                255.76708533

      Distance between last two positions (km):           0.00000000
      Velocity difference magnitude  (km/s):           0.00000000

      Frame evaluation locus:   OBSERVER

      Observer:                 MGS
      Observation time:         2003 OCT 13 06:00:00.000000 UTC
      Target center:            MARS
      Target-center state time: 2000 JAN 01 12:00:00.000000 TDB
      Target frame:             IAU_MARS
      Emission time:            2003 OCT 13 05:59:59.998702 UTC
      Output reference frame:   MGS_MOC_NA
      Aberration correction:    CN+S
      Observer-target position (km):
               0.00000001          -0.00000001         388.97573572
      Observer-target velocity (km/s):
               2.91968665           0.15140014           0.92363513
      Light time (s):                  0.00129748
      Target range from cspice_sincpt (km):         388.97573572

Particulars


   This routine computes observer-target states for targets whose
   trajectories are not provided by SPK files.

   Targets supported by this routine must have constant velocity
   with respect to a specified center of motion, expressed in a
   caller-specified reference frame. The state of the center of
   motion relative to the observer must be computable using
   loaded SPK data.

   For applications in which the target has zero velocity
   relative to its center of motion, the CSPICE routine

      cspice_spkcpt     { SPK, constant position target }

   can be used. cspice_spkcpt has a simpler interface than that
   of cspice_spkcvt.

   This routine is suitable for computing states of landmarks on the
   surface of an extended object, as seen by a specified observer,
   in cases where no SPK data are available for those landmarks.

   This routine's treatment of the output reference frame differs
   from that of the principal SPK API routines

      cspice_spkezr
      cspice_spkpos

   which require both observer and target ephemerides to be provided
   by loaded SPK files:

      The SPK API routines listed above evaluate the orientation of
      the output reference frame (with respect to the J2000 frame)
      at an epoch corrected for one-way light time between the
      observer and the center of the output frame. When the center
      of the output frame is not the target (for example, when the
      target is on the surface of Mars and the output frame is
      centered at Mars' center), the epoch of evaluation may not
      closely match the light-time corrected epoch associated with
      the target itself.

      This routine allows the caller to dictate how the orientation
      of the output reference frame is to be evaluated. The caller
      passes to this routine an input string called the output
      frame's evaluation "locus." This string specifies the location
      associated with the output frame's evaluation epoch. The three
      possible values of the locus are

         'TARGET'
         'OBSERVER'
         'CENTER'

      The choice of locus has an effect when aberration corrections
      are used and the output frame is non-inertial.

      When the locus is 'TARGET' and light time corrections are used,
      the orientation of the output frame is evaluated at the epoch
      obtained by correcting the observation epoch 'et' for one-way
      observer-target light time 'ltime'. The evaluation epoch will be
      either et-ltime or et+ltime for reception or transmission corrections
      respectively.

      For remote sensing applications where the target is a surface
      point on an extended object, and the orientation of that
      object should be evaluated at the emission time, the locus
      'TARGET' should be used.

      When the output frame's orientation should be evaluated at
      the observation epoch 'et', which is the case when the
      output frame is centered at the observer, the locus
      'OBSERVER' should be used.

      The locus option 'CENTER' is provided for compatibility
      with existing SPK state computation APIs such as cspice_spkezr.

      Note that the output frame evaluation locus does not affect
      the computation of light time between the target and
      observer.


   The SPK routines that compute observer-target states for
   combinations of objects having ephemerides provided by SPK files and
   objects having constant position or constant velocity are

      cspice_spkcpo {SPK, Constant position observer}
      cspice_spkcpt {SPK, Constant position target}
      cspice_spkcvo {SPK, Constant velocity observer}
      cspice_spkcvt {SPK, Constant velocity target}

Required Reading


   For important details concerning this module's function, please refer to
   the CSPICE routine spkcvt_c.

   MICE.REQ
   FRAMES.REQ
   PCK.REQ
   SPK.REQ
   TIME.REQ

Version


   -Mice Version 1.0.0, 11-JUN-2013, EDW (JPL)

Index_Entries


   state of constant_velocity_target
   state of surface_point on extended_object
   state of landmark on extended_object


Wed Apr  5 18:00:34 2017