void tipbod_c ( ConstSpiceChar * ref,
SpiceInt body,
SpiceDouble et,
SpiceDouble tipm[3][3] )
Return a 3x3 matrix that transforms positions in inertial
coordinates to positions in body-equator-and-prime-meridian
coordinates.
PCK
NAIF_IDS
ROTATION
TIME
TRANSFORMATION
ROTATION
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
ref I ID of inertial reference frame to transform from.
body I ID code of body.
et I Epoch of transformation.
tipm O Transformation (position), inertial to prime
meridian.
ref is the NAIF name for an inertial reference frame.
Acceptable names include:
Name Description
-------- --------------------------------
"J2000" Earth mean equator, dynamical
equinox of J2000
"B1950" Earth mean equator, dynamical
equinox of B1950
"FK4" Fundamental Catalog (4)
"DE-118" JPL Developmental Ephemeris (118)
"DE-96" JPL Developmental Ephemeris ( 96)
"DE-102" JPL Developmental Ephemeris (102)
"DE-108" JPL Developmental Ephemeris (108)
"DE-111" JPL Developmental Ephemeris (111)
"DE-114" JPL Developmental Ephemeris (114)
"DE-122" JPL Developmental Ephemeris (122)
"DE-125" JPL Developmental Ephemeris (125)
"DE-130" JPL Developmental Ephemeris (130)
"GALACTIC" Galactic System II
"DE-200" JPL Developmental Ephemeris (200)
"DE-202" JPL Developmental Ephemeris (202)
(See the routine CHGIRF for a full list of names.)
The output tipm will give the transformation
from this frame to the bodyfixed frame specified by
body at the epoch specified by et.
body is the integer ID code of the body for which the
position transformation matrix is requested. Bodies
are numbered according to the standard NAIF
numbering scheme. The numbering scheme is
explained in the NAIF_IDS required reading file.
et is the epoch at which the position transformation
matrix is requested. (This is typically the
epoch of observation minus the one-way light time
from the observer to the body at the epoch of
observation.)
tipm is a 3x3 coordinate transformation matrix. It is
used to transform positions from inertial coordinates to
body fixed (also called equator and prime meridian)
coordinates.
Given a position P in the inertial reference frame
specified by ref, the corresponding bodyfixed
position is given by the matrix vector product
tipm * s
The X axis of the PM system is directed to the
intersection of the equator and prime meridian.
The Z axis points along the spin axis and points
towards the same side of the invariable plane of
the solar system as does earth's north pole.
None.
1) If the kernel pool does not contain all of the data required
for computing the transformation matrix, tipm, the error
SPICE(INSUFFICIENTANGLES) is signalled.
2) If the reference frame ref is not recognized, a routine
called by tipbod_c will diagnose the condition and signal an
error.
3) If the code body is not recognized, the error is diagnosed by a
routine called by tipbod_c.
4) If the input string pointer is null, the error
SPICE(NULLPOINTER) will be signaled.
5) If the input string has length zero, the error
SPICE(EMPTYSTRING) will be signaled.
None.
tipbod_c takes PCK information as input, either in the form of a
binary or text PCK file. If the data required to compute tipm are
available in a binary PCK, these data will take precedence over data
from a text PCK. If there are multiple binary PCKs containing data
from which tipm can be computed, the last loaded PCK takes
precedence. If binary PCK data are available for the requested body
and time, the Euler angles giving the body's orientation are
evaluated, and the transformation matrix tipm is calculated from
them. Using the Euler angles PHI, DELTA and W we compute
TIPM = [W] [DELTA] [PHI]
3 1 3
If no appropriate binary PCK files have been loaded, text PCK data
are used. Here information is found as RA, DEC and W (with the
possible addition of nutation and libration terms for satellites).
Again, the Euler angles are found, and the transformation matrix is
calculated from them. The transformation from inertial to
bodyfixed coordinates is represented as:
TIPM = [W] [HALFPI-DEC] [RA+HALFPI]
3 1 3
These Euler angles RA, DEC and W are related to PHI, DELTA and W
by the equations
RA = PHI - pi/2
DEC = pi/2 - DELTA
W = W
In the text file, RA, DEC, and W are defined as follows:
2 ____
RA2*t \
RA = RA0 + RA1*t/T + ------ + / a sin theta
2 ---- i i
T i
2 ____
DEC2*t \
DEC = DEC0 + DEC1*t/T + ------- + / d cos theta
2 ---- i i
T i
2 ____
W2*t \
W = W0 + W1*t/d + ----- + / w sin theta
2 ---- i i
d i
where:
d = seconds/day
T = seconds/Julian century
a , d , and w arrays apply to satellites only.
i i i
theta = THETA0(i) + THETA1(i)*t/T are specific to each
i
planet.
These angles---typically nodal rates---vary in number and
definition from one planetary system to the next.
Note that the items necessary to compute the Euler angles
must have been loaded into the kernel pool (by one or more
previous calls to furnsh_c). The Euler angles are typically
stored in the P_constants kernel file that comes with
CSPICE.
1) In the following code fragment, tipbod_c is used to transform
a position in J2000 inertial coordinates to a position in
bodyfixed coordinates.
The 3-vector postn represents the inertial position
of an object with respect to the center of the
body at time et.
#include "SpiceUsr.h"
.
.
.
/.
First load the kernel pool.
./
furnsh_c ( "PLANETARY_CONSTANTS.KER" );
/.
Next get the transformation.
./
tipbod_c ( "J2000", body, et, tipm );
/.
Convert position to bodyfixed coordinates.
./
mxv_c ( tipm, postn, bfxpos );
The kernel pool must be loaded with the appropriate
coefficients (from the P_constants kernel or binary PCK file)
prior to calling this routine.
None.
N.J. Bachman (JPL)
W.L. Taber (JPL)
K.S. Zukor (JPL)
-CSPICE Version 1.0.2, 14-AUG-2006 (EDW)
Replace mention of ldpool_c with furnsh_c.
-CSPICE Version 1.0.1, 13-APR-2000 (NJB)
Made some minor updates and corrections in the code example.
-CSPICE Version 1.0.0, 08-FEB-1998 (NJB)
Based on SPICELIB Version 1.0.3, 10-MAR-1994 (KSZ).
transformation from inertial position to bodyfixed
Link to routine tipbod_c source file tipbod_c.c
|