spkw15_c

Index Page spkw15_c
A B C D E F G H I J K L M N O P Q R S T U V W X
Procedure Abstract Required_Reading Keywords Brief_I/O Detailed_Input | Detailed_Output Parameters Exceptions Files Particulars Examples | Restrictions Literature_References Author_and_Institution Version Index_Entries
#### Procedure
       void spkw15_c ( SpiceInt           handle,
                       SpiceInt           body,
                       SpiceInt           center,
                       ConstSpiceChar   * frame,
                       SpiceDouble        first,
                       SpiceDouble        last,
                       ConstSpiceChar   * segid,
                       SpiceDouble        epoch,
                       ConstSpiceDouble   tp     [3],
                       ConstSpiceDouble   pa     [3],
                       SpiceDouble        p,
                       SpiceDouble        ecc,
                       SpiceDouble        j2flg,
                       ConstSpiceDouble   pv     [3],
                       SpiceDouble        gm,
                       SpiceDouble        j2,
                       SpiceDouble        radius     )
#### Abstract
       Write an SPK segment of type 15 given a type 15 data record.
#### Required_Reading
       SPK
#### Keywords
       EPHEMERIS
#### Brief_I/O
       Variable  I/O  Description
       --------  ---  --------------------------------------------------
       handle     I   Handle of an SPK file open for writing.
       body       I   Body code for ephemeris object.
       center     I   Body code for the center of motion of the body.
       frame      I   The reference frame of the states.
       first      I   First valid time for which states can be computed.
       last       I   Last valid time for which states can be computed.
       segid      I   Segment identifier.
       epoch      I   Epoch of the periapse.
       tp         I   Trajectory pole vector.
       pa         I   Periapsis vector.
       p          I   Semi-latus rectum.
       ecc        I   Eccentricity.
       j2flg      I   J2 processing flag.
       pv         I   Central body pole vector.
       gm         I   Central body GM.
       j2         I   Central body J2.
       radius     I   Equatorial radius of central body.
#### Detailed_Input
                All units are radians, km, seconds.

       handle      is the file handle of an SPK file that has been
                   opened for writing.

       body        is the NAIF ID for the body whose states are
                   to be recorded in an SPK file.

       center      is the NAIF ID for the center of motion associated
                   with body.

       frame       is the reference frame that states are referenced to,
                   for example "J2000".

       first       are the bounds on the ephemeris times, expressed as
       last        seconds past J2000.

       segid       is the segment identifier. An SPK segment identifier
                   may contain up to 40 characters.

       epoch       is the epoch of the orbit elements at periapse
                   in ephemeris seconds past J2000.

       tp          is a unit vector parallel to the angular momentum
                   vector of the orbit at epoch expressed relative to
                   frame.

       pa          is a unit vector parallel to the position vector
                   of the trajectory at periapsis of epoch expressed
                   relative to frame.

       p           is the semi-latus rectum---p in the equation:

                      r = p/(1 + ecc*cos(Nu))

       ecc          is the eccentricity.

       j2flg        is the J2 processing flag describing what J2
                    corrections are to be applied when the orbit is
                    propagated.

                    All J2 corrections are applied if the value of j2flg
                    is not 1, 2 or 3.

                    If the value of the flag is 3 no corrections are
                    done.

                    If the value of the flag is 1 no corrections are
                    computed for the precession of the line of apsides.
                    However, regression of the line of nodes is
                    performed.

                    If the value of the flag is 2 no corrections are
                    done for the regression of the line of nodes.
                    However, precession of the line of apsides is
                    performed.

                    Note that J2 effects are computed only if the orbit
                    is elliptic and does not intersect the central body.

       pv           is a unit vector parallel to the north pole vector
                    of the central body expressed relative to frame.

       gm           is the central body gm.

       j2           is the central body J2 (dimensionless).

       radius       is the equatorial radius of the central body.
#### Detailed_Output
       None.  A type 15 segment is written to the file attached
       to handle.
#### Parameters
       None.
#### Exceptions
       1)  If the eccentricity is less than zero, the error
           SPICE(BADECCENTRICITY) will be signaled.

       2)  If the semi-latus rectum is 0, the error
           SPICE(BADLATUSRECTUM) is signaled.

       3)  If the pole vector, trajectory pole vector or periapsis vector
           have zero length, the error SPICE(BADVECTOR) is signaled.

       4)  If the trajectory pole vector and the periapsis vector are
           not orthogonal, the error SPICE(BADINITSTATE) is signaled.
           The test for orthogonality is very crude.  The routine simply
           checks that the dot product of the unit vectors parallel
           to the trajectory pole and periapse vectors is less than
           0.00001.  This check is intended to catch blunders, not to
           enforce orthogonality to double precision capacity.

       5)  If the mass of the central body is non-positive, the error
           SPICE(NONPOSITIVEMASS) is signaled.

       6)  If the radius of the central body is negative, the error
           SPICE(BADRADIUS) is signaled.

       7)  If the segment identifier has more than 40 non-blank characters
           the error SPICE(SEGIDTOOLONG) is signaled.

       8)  If the segment identifier contains non-printing characters
           the error SPICE(NONPRINTABLECHARS) is signaled.

       9)  If there are inconsistencies in the body, center, frame or
           first and last times, the problem will be diagnosed by
           a routine in the call tree of this routine.

       10) If either the input frame or segment ID string pointer is null,
           the error SPICE(NULLPOINTER) is signaled.

       11) If either the input frame or segment ID string is empty,
           the error SPICE(EMPTYSTRING) is signaled.
#### Files
       A new type 15 SPK segment is written to the SPK file attached
       to handle.
#### Particulars
       This routine writes an SPK type 15 data segment to the open SPK
       file according to the format described in the type 15 section of
       the SPK Required Reading. The SPK file must have been opened with
       write access.

       This routine is provided to provide direct support for the MASL
       precessing orbit formulation.
#### Examples
       Suppose that at time epoch you have the J2000 periapsis
       state of some object relative to some central body and would
       like to create a type 15 SPK segment to model the motion of
       the object using simple regression and precession of the
       line of nodes and apsides. The following code fragment
       illustrates how you can prepare such a segment.  We shall
       assume that you have in hand the J2000 direction of the
       central body's pole vector, its GM, J2 and equatorial
       radius.  In addition we assume that you have opened an SPK
       file for write access and that it is attached to handle.

       (If your state is at an epoch other than periapse the
       fragment below will NOT produce a "correct" type 15 segment
       for modelling the motion of your object.)

          #include "SpiceUsr.h"
              .
              .
              .

          /.
          First we get the osculating elements.
          /
          oscelt_c ( state, epoch, gm, elts );

          /.
          From these collect the eccentricity and semi-latus rectum.
          ./
          ecc = elts [ 1 ];
          p   = elts [ 0 ] * ( 1.0 + ecc );

          /.
          Next get the trajectory pole vector and the
          periapsis vector.
          ./
          ucrss_c ( state, state+4, tp );
          vhat_c  ( state,          pa );

          /.
          Enable both J2 corrections.
          ./
          j2flg = 0.0;

          /.
          Now add the segment.
          ./
          spkw15_c ( handle,  body,   center,  frame,  first,  last,
                     segid,   epoch,  tp,      pa,     p,      ecc,
                     j2flg,   pv,     gm,      j2,     radius       );
#### Restrictions
       None.
#### Literature_References
       None.
#### Author_and_Institution
       W.L. Taber      (JPL)
#### Version
       -CSPICE Version 1.0.0, 21-JUN-1999
#### Index_Entries
       Write a type 15 spk segment
#### Link to routine spkw15_c source file spkw15_c.c

    Thu Apr 16 08:59:17 2009