Table of contents
CSPICE_SPKW17 writes an SPK segment of type 17 given a type 17 data
record.
Given:
handle the scalar integer file handle of an SPK file that has been
opened for writing.
help, handle
LONG = Scalar
body the scalar integer NAIF ID for the body whose states are to be
recorded in the SPK file.
help, body
LONG = Scalar
center the scalar integer NAIF ID for the center of motion associated
with body.
help, center
LONG = Scalar
frame the scalar string reference frame name that states are
referenced to, for example 'J2000'.
help, frame
STRING = Scalar
first,
last the scalar double precision bounds on the ephemeris times,
expressed as seconds past J2000.
help, first
DOUBLE = Scalar
help, last
DOUBLE = Scalar
segid the scalar string segment identifier.
help, segid
STRING = Scalar
An SPK segment identifier may contain up to 40 characters.
epoch the scalar double precision epoch of equinoctial elements in
seconds past the J2000 epoch.
help, epoch
DOUBLE = Scalar
eqel an array of 9 double precision numbers that are the equinoctial
elements for some orbit relative to the equatorial frame of a
central body.
help, eqel
DOUBLE = Array[9]
Note: The Z-axis of the equatorial frame is the
direction of the pole of the central body relative
to `frame'. The X-axis is given by the cross product of
the Z-axis of `frame' with the direction of the pole of
the central body. The Y-axis completes a right handed
frame.
The specific arrangement of the elements is spelled
out below. The following terms are used in the
discussion of elements of `eqel':
inc --- inclination of the orbit
argp --- argument of periapse
node --- longitude of the ascending node
e --- eccentricity of the orbit
m0 --- mean anomaly
eqel[0] is the semi-major axis (A) of the orbit in km.
eqel[1] is the value of H at the specified epoch:
H = e * sin( argp + node )
eqel[2] is the value of K at the specified epoch:
K = e * cos( argp + node )
eqel[3] is the mean longitude at the epoch of the
elements measured in radians:
( m0 + argp + node )
eqel[4] is the value of P at the specified epoch:
P = tan( inc/1 ) * sin( node )
eqel[5] is the value of Q at the specified epoch:
Q = tan( inc/1 ) * cos( node );
eqel[6] is the rate of the longitude of periapse
at the epoch of the elements.
( dargp/dt + dnode/dt )
This rate is assumed to hold for all time. The
rate is measured in radians per second.
eqel[7] is the derivative of the mean longitude:
( dm0/dt + dargp/dt + dnode/dt )
This rate is assumed to be constant and is
measured in radians/second.
eqel[8] is the rate of the longitude of the ascending
node:
( dnode/dt )
This rate is measured in radians per second.
rapol the Right Ascension of the pole of the reference plane relative
to `frame' measured in radians.
help, rapol
DOUBLE = Scalar
decpol the declination of the pole of the reference plane relative to
`frame' measured in radians.
help, decpol
DOUBLE = Scalar
the call:
cspice_spkw17, handle, body, center, frame, first, last, $
segid, epoch, eqel, rapol, decpol
writes an SPK type 17 segment to the file attached to `handle'.
None.
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.
1) Suppose that at a given time you have the classical elements
of Daphnis relative to the equatorial frame of Saturn. These
can be converted to equinoctial elements and stored in an SPK
file as a type 17 segment so that Daphnis can be used within
the SPK subsystem of the SPICE system.
The example code shown below creates an SPK type 17 kernel
with a single segment using such data.
Example code begins here.
PRO spkw17_ex1
;;
;; Local parameters.
;;
SPK17 = 'spkw17_ex1.bsp'
;;
;; The SPK type 17 segment will contain data for Daphnis
;; (ID 635) with respect to Saturn (ID 699) in the J2000
;; reference frame.
;;
BODY = 635L
CENTER = 699L
FRMNAM = 'J2000'
;;
;; This is the list of parameters used to represent the
;; classical elements:
;;
;; Variable Meaning
;; -------- ---------------------------------------
;; A Semi-major axis in km.
;; ECC Eccentricity of orbit.
;; INC Inclination of orbit.
;; NODE Longitude of the ascending node at
;; epoch.
;; OMEGA Argument of periapse at epoch.
;; M Mean anomaly at epoch.
;; DMDT Mean anomaly rate in radians/second.
;; DNODE Rate of change of longitude of
;; ascending node in radians/second.
;; DOMEGA Rate of change of argument of periapse
;; in radians/second.
;; EPOCH The epoch of the elements in seconds
;; past the J2000 epoch.
;;
A = 1.36505608D+05
ECC = -2.105898062D-05
INC = -3.489710429D-05
NODE = -3.349237456D-02
OMEGA = 1.52080206722D0
M = 1.21177109734D0
DMDT = 1.218114014D-04
DNODE = -5.96845468D-07
DOMEGA = 1.196601093D-06
EPOCH = 0.D0
;;
;; In addition, the cspice_spkw17 routine requires the Right
;; Ascension and Declination of the pole of the
;; reference plane relative to the J2000 frame, in radians.
;;
RAPOL = 7.08332284D-01
DECPOL = 1.45800286D0
;;
;; Set the start and end times of interval covered by
;; segment.
;;
first = 504878400.D0
last = 1578657600.D0
;;
;; `ncomch' is the number of characters to reserve for the
;; kernel's comment area. This example doesn't write
;; comments, so set to zero.
;;
ncomch = 0L
;;
;; Internal file name and segment ID.
;;
ifname = 'Test for type 17 SPK internal file name'
segid = 'SPK type 17 test segment'
;;
;; Open a new SPK file.
;;
cspice_spkopn, SPK17, ifname, ncomch, handle
;;
;; Convert the classical elements to equinoctial elements
;; (in the order compatible with type 17).
;;
eqel = [ A, $
ECC * sin ( OMEGA + NODE ), $
ECC * cos ( OMEGA + NODE ), $
M + OMEGA + NODE, $
tan( INC/2.D0 ) * sin( NODE ), $
tan( INC/2.D0 ) * cos( NODE ), $
DOMEGA + DNODE, $
DMDT + DOMEGA + DNODE, $
DNODE ]
;;
;; Now add the segment.
;;
cspice_spkw17, handle, BODY, CENTER, FRMNAM, first, last, $
segid, EPOCH, eqel, RAPOL, DECPOL
;;
;; Close the SPK file.
;;
cspice_spkcls, handle
END
When this program is executed, no output is presented on
screen. After run completion, a new SPK type 17 exists in
the output directory.
This routine writes an SPK type 17 data segment to the open SPK
file according to the format described in the type 17 section of
the SPK Required Reading. The SPK file must have been opened with
write access.
1) If the semi-major axis is less than or equal to zero, the
error SPICE(BADSEMIAXIS) is signaled by a routine in the call
tree of this routine.
2) If the eccentricity of the orbit corresponding to the values
of H and K ( eqel[1] and eqel[2] ) is greater than 0.9, the
error SPICE(ECCOUTOFRANGE) is signaled by a routine in the
call tree of this routine.
3) If the segment identifier has more than 40 non-blank
characters, the error SPICE(SEGIDTOOLONG) is signaled by a
routine in the call tree of this routine.
4) If the segment identifier contains non-printing characters,
the error SPICE(NONPRINTABLECHARS) is signaled by a routine in
the call tree of this routine.
5) If there are inconsistencies in the `body', `center', `frame' or
`first' and `last' times, an error is signaled by a routine in
the call tree of this routine.
6) If any of the input arguments, `handle', `body', `center',
`frame', `first', `last', `segid', `epoch', `eqel', `rapol' or
`decpol', is undefined, an error is signaled by the IDL error
handling system.
7) If any of the input arguments, `handle', `body', `center',
`frame', `first', `last', `segid', `epoch', `eqel', `rapol' or
`decpol', is not of the expected type, or it does not have the
expected dimensions and size, an error is signaled by the Icy
interface.
A new type 17 SPK segment is written to the SPK file attached
to `handle'.
None.
ICY.REQ
SPK.REQ
None.
J. Diaz del Rio (ODC Space)
E.D. Wright (JPL)
-Icy Version 1.0.1, 01-JUN-2021 (JDR)
Edited the header to comply with NAIF standard. Added complete
code examples based on existing example, with modified input data.
Added -Parameters, -Exceptions, -Files, -Restrictions,
-Literature_References and -Author_and_Institution sections.
Removed reference to the routine's corresponding CSPICE header from
-Abstract section.
Added arguments' type and size information in the -I/O section.
-Icy Version 1.0.0, 07-NOV-2011 (EDW)
Write a type 17 SPK segment
|