CSPICE_SPKSFS searches through loaded SPK files to find the
highest-priority segment applicable to the body and time specified.
body the SPK ID code of an ephemeris object, typically a solar
[1,1] = size(dc); int32 = class(body)
et the time, in seconds past the epoch J2000 TDB.
[1,1] = size(et); double = class(et)
[handle, descr, ident, found] = cspice_spksfs( body, et)
handle the handle of the SPK file containing a located segment.
[1,1] = size(handle); int32 = class(handle)
descr the descriptor of a located SPK segment.
[5,1] = size(descr); double = class(descr)
ident the string SPK segment identifier of a located SPK segment.
[1,c1] = size(ident); char = class(ident)
found indicates whether a requested segment was found or not.
The other output arguments are valid only if `found'
is set to true.
[1,1] = size(found); logical = class(found)
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.
In the following code fragment, an SPK file is searched for
a segment containing ephemeris data for the Jupiter system
barycenter at a particular epoch. Using this segment,
states of the Jupiter system barycenter relative to the
solar system barycenter are evaluated at a sequence of times.
This method of state computation minimizes the number of
segment searches required to obtain requested data, but
it bypasses the SPK subsystem's state chaining mechanism.
Use the meta-kernel shown below to load the required SPICE
File name: standard.tm
This meta-kernel is intended to support operation of SPICE
example programs. The kernels shown here should not be
assumed to contain adequate or correct versions of data
required by SPICE-based user applications.
In order for an application to use this meta-kernel, the
kernels referenced here must be present in the user's
current working directory.
The names and contents of the kernels referenced
by this meta-kernel are as follows:
File name Contents
de421.bsp Planetary ephemeris
pck00010.tpc Planet orientation and
KERNELS_TO_LOAD = ( 'de421.bsp',
% Local constants
META = 'standard.tm';
ND = 2;
NI = 6;
TIMFMT = 'YYYY MON DD HR:MN:SC.######::TDB TDB';
% Load meta-kernel.
cspice_furnsh( META )
% Convert starting time to seconds past J2000 TDB.
timstr = '2012 APR 27 00:00:00.000 TDB';
et0 = cspice_str2et(timstr);
% Find a loaded segment for the Jupiter barycenter
% that covers `et0'.
body = 5;
[handle, descr, segid, found] = cspice_spksfs( body, et0);
txt = sprintf( 'No SPK segment found for body %d at time %s', ...
body, timstr );
error( txt )
% Unpack the descriptor of the current segment.
[dc, ic] = cspice_dafus( descr, ND, NI );
frname = cspice_frmnam( ic(3) );
fprintf( 'Body = %d\n', ic(1) )
fprintf( 'Center = %d\n', ic(2) )
fprintf( 'Frame = %s\n', frname)
fprintf( 'Data type = %d\n', ic(4) )
fprintf( 'Start ET = %f\n', dc(1) )
fprintf( 'Stop ET = %f\n', dc(2) )
fprintf( 'Segment ID = %s\n\n', segid )
% Evaluate states at 10-second steps, starting at `et0'
% and continuing for 20 seconds.
et = et0 + ( 10. * (i-1) );
% Convert `et' to a string for display.
outstr = cspice_timout( et, TIMFMT );
% Attempt to compute a state only if the segment's
% coverage interval contains `et'.
if ( et <= dc(2) )
% This segment has data at `et'. Evaluate the
% state of the target relative to its center
% of motion.
[ref_id, state, center] = cspice_spkpvn( handle, descr, et );
% Display the time and state.
fprintf( '\n%s\n', outstr )
fprintf( 'Position X (km): %24.17f\n', state(1) )
fprintf( 'Position Y (km): %24.17f\n', state(2) )
fprintf( 'Position Z (km): %24.17f\n', state(3) )
fprintf( 'Velocity X (km): %24.17f\n', state(4) )
fprintf( 'Velocity X (km): %24.17f\n', state(5) )
fprintf( 'Velocity X (km): %24.17f\n', state(6) )
txt = sprintf( 'No data found for body %d at time %s', ...
body, outstr );
error( txt )
% It's always good form to unload kernels after use,
% particularly in IDL due to data persistence.
Body = 5
Center = 0
Frame = J2000
Data type = 2
Start ET = -3169195200.000000
Stop ET = 1696852800.000000
Segment ID = DE-0421LE-0421
2012 APR 27 00:00:00.000000 TDB
Position X (km): 464528993.98216485977172852
Position Y (km): 541513126.15685200691223145
Position Z (km): 220785135.62462940812110901
Velocity X (km): -10.38685648307654930
Velocity X (km): 7.95324700713742416
Velocity X (km): 3.66185835431306517
2012 APR 27 00:00:10.000000 TDB
Position X (km): 464528890.11359262466430664
Position Y (km): 541513205.68931341171264648
Position Z (km): 220785172.24320945143699646
Velocity X (km): -10.38685796160419272
Velocity X (km): 7.95324528430304944
Velocity X (km): 3.66185765185608103
2012 APR 27 00:00:20.000000 TDB
Position X (km): 464528786.24500560760498047
Position Y (km): 541513285.22175765037536621
Position Z (km): 220785208.86178246140480042
Velocity X (km): -10.38685944013147910
Velocity X (km): 7.95324356146845002
Velocity X (km): 3.66185694939899253
This routine finds the highest-priority segment, in any loaded
SPK file, such that the segment provides data for the specified
body and epoch.
For important details concerning this module's function, please refer to
the CSPICE routine spksfs_c.
-Mice Version 1.0.0, 30-OCT-2012, EDW (JPL)
select spk file and segment