void pxform_c ( ConstSpiceChar * from,
ConstSpiceChar * to,
SpiceDouble rotate )
Return the matrix that transforms position vectors from one
specified frame to another at a specified epoch.
VARIABLE I/O DESCRIPTION
-------- --- --------------------------------------------------
from I Name of the frame to transform from.
to I Name of the frame to transform to.
et I Epoch of the rotation matrix.
rotate O A rotation matrix.
from is the name of a reference frame in which a position
vector is known.
to is the name of a reference frame in which it is desired
to represent a position vector.
et is the epoch in ephemeris seconds past the epoch of
J2000 (TDB) at which the position transformation matrix
`rotate' should be evaluated.
rotate is the matrix that transforms position vectors from the
reference frame `from' to the frame `to' at epoch `et'.
If (x, y, z) is a position relative to the frame `from'
then the vector ( x', y', z') is the same position
relative to the frame `to' at epoch `et'. Here the
vector ( x', y', z' ) is defined by the equation:
- - - - - -
| x' | | | | x |
| y' | = | rotate | | y |
| z' | | | | z |
- - - - - -
1) If sufficient information has not been supplied via loaded SPICE
kernels to compute the transformation between the two frames, the
error will be diagnosed by a routine in the call tree of this
2) If either frame `from' or `to' is not recognized the error
SPICE(UNKNOWNFRAME) will be signaled.
This routine provides the user level interface to computing
position transformations from one reference frame to another.
Note that the reference frames may be inertial or non-inertial.
However, the user must take care that sufficient SPICE kernel
information is loaded to provide a complete position
transformation path from the from frame to the to frame.
Suppose that you have geodetic coordinates of a station on the
surface of the earth and that you need the inertial (J2000)
position of this station. The following code fragment
illustrates how to transform the position of the station to a
bodvcd_c ( 399, radii, 3, &n, abc );
equatr = abc;
polar = abc;
f = ( equatr - polar ) / equatr;
georec_c ( long, lat, 0.0, equatr, f, epos );
pxform_c ( "IAU_EARTH", "J2000", et, rotate );
mxv_c ( rotate, epos, jpos );
The position jpos is the desired J2000 position of the station.
C.H. Acton (JPL)
N.J. Bachman (JPL)
B.V. Semenov (JPL)
W.L. Taber (JPL)
-CSPICE Version 1.0.4, 27-FEB-2008 (BVS)
Added FRAMES to the Required_Reading section of the header.
-CSPICE Version 1.0.3, 24-OCT-2005 (NJB)
Header updates: example had invalid flattening factor
computation; this was corrected. Reference to bodvar_c was
replaced with reference to bodvcd_c.
-CSPICE Version 1.0.2, 07-JAN-2004 (EDW)
Trivial typo correction to example section.
-CSPICE Version 1.0.1, 29-JUL-2003 (NJB) (CHA)
Various header corrections were made.
-CSPICE Version 1.0.0, 20-JUN-1999 (NJB) (WLT)
Find a position transformation matrix