| eul2xf_c |
|
Table of contents
Procedure
eul2xf_c ( Euler angles and derivative to transformation )
void eul2xf_c ( ConstSpiceDouble eulang[6],
SpiceInt axisa,
SpiceInt axisb,
SpiceInt axisc,
SpiceDouble xform [6][6] )
AbstractCompute a state transformation from an Euler angle factorization of a rotation and the derivatives of those Euler angles. Required_ReadingROTATION KeywordsANGLES DERIVATIVES STATE Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- eulang I An array of Euler angles and their derivatives. axisa I Axis A of the Euler angle factorization. axisb I Axis B of the Euler angle factorization. axisc I Axis C of the Euler angle factorization. xform O A state transformation matrix. Detailed_Input
eulang is the set of Euler angles corresponding to the
specified factorization.
If we represent `r' as shown here:
r = [ alpha ] [ beta ] [ gamma ]
axisa axisb axisc
then
eulang[0] = alpha
eulang[1] = beta
eulang[2] = gamma
eulang[3] = dalpha/dt
eulang[4] = dbeta/dt
eulang[5] = dgamma/dt
axisa,
axisb,
axisc are the axes desired for the factorization of `r'.
All must be in the range from 1 to 3. Moreover
it must be the case that `axisa' and `axisb' are distinct
and that `axisb' and `axisc' are distinct.
Every rotation matrix can be represented as a product
of three rotation matrices about the principal axes
of a reference frame.
r = [ alpha ] [ beta ] [ gamma ]
axisa axisb axisc
The value 1 corresponds to the X axis.
The value 2 corresponds to the Y axis.
The value 3 corresponds to the Z axis.
Detailed_Output
xform is the state transformation matrix corresponding to `r'
and dr/dt as described above. Pictorially,
.- -.
| | |
| r | 0 |
| | |
|-------+-------|
| | |
| dr/dt | r |
| | |
`- -'
where `r' is a rotation matrix that varies with respect to
time and dr/dt is its time derivative.
ParametersNone. Exceptions
1) If any of `axisa', `axisb', or `axisc' do not have values in
{ 1, 2, 3 }
an error is signaled by a routine in the call tree of this
routine.
FilesNone. Particulars
A word about notation: the symbol
[ x ]
i
indicates a coordinate system rotation of x radians about the
ith coordinate axis. To be specific, the symbol
[ x ]
1
indicates a coordinate system rotation of x radians about the
first, or x-, axis; the corresponding matrix is
.- -.
| 1 0 0 |
| |
| 0 cos(x) sin(x) |
| |
| 0 -sin(x) cos(x) |
`- -'
Remember, this is a COORDINATE SYSTEM rotation by x radians; this
matrix, when applied to a vector, rotates the vector by -x
radians, not x radians. Applying the matrix to a vector yields
the vector's representation relative to the rotated coordinate
system.
The analogous rotation about the second, or y-, axis is
represented by
[ x ]
2
which symbolizes the matrix
.- -.
| cos(x) 0 -sin(x) |
| |
| 0 1 0 |
| |
| sin(x) 0 cos(x) |
`- -'
and the analogous rotation about the third, or z-, axis is
represented by
[ x ]
3
which symbolizes the matrix
.- -.
| cos(x) sin(x) 0 |
| |
| -sin(x) cos(x) 0 |
| |
| 0 0 1 |
`- -'
The input matrix is assumed to be the product of three
rotation matrices, each one of the form
.- -.
| 1 0 0 |
| |
| 0 cos(r) sin(r) | (rotation of r radians about the
| | x-axis),
| 0 -sin(r) cos(r) |
`- -'
.- -.
| cos(s) 0 -sin(s) |
| |
| 0 1 0 | (rotation of s radians about the
| | y-axis),
| sin(s) 0 cos(s) |
`- -'
or
.- -.
| cos(t) sin(t) 0 |
| |
| -sin(t) cos(t) 0 | (rotation of t radians about the
| | z-axis),
| 0 0 1 |
`- -'
where the second rotation axis is not equal to the first or
third. Any rotation matrix can be factored as a sequence of
three such rotations, provided that this last criterion is met.
This routine is intended to provide an inverse for xf2eul_c.
The two function calls shown here will not change
`xform' except for round off errors.
xf2eul_c ( xform, axisa, axisb, axisc, eulang, &unique );
eul2xf_c ( eulang, axisa, axisb, axisc, xform );
On the other hand the two calls
eul2xf_c ( eulang, axisa, axisb, axisc, xform );
xf2eul_c ( xform, axisa, axisb, axisc, eulang, &unique );
will leave `eulang' unchanged only if the components of `eulang'
are in the range produced by xf2eul_c and the Euler representation
of the rotation component of `xform' is unique within that range.
Examples
The numerical results shown for this example may differ across
platforms. The results depend on the SPICE kernels used as
input, the compiler and supporting libraries, and the machine
specific arithmetic implementation.
1) Suppose you have a set of Euler angles and their derivatives
for a 3 1 3 rotation, and that you would like to determine
the equivalent angles and derivatives for a 1 2 3 rotation.
r = [alpha] [beta] [gamma]
3 1 3
r = [roll] [pitch] [yaw]
1 2 3
The following code example will perform the desired
computation.
Example code begins here.
/.
Program eul2xf_ex1
./
#include <stdio.h>
#include "SpiceUsr.h"
int main( )
{
/.
Local variables.
./
SpiceDouble abgang [6];
SpiceDouble rpyang [6];
SpiceDouble xform [6][6];
SpiceBoolean unique;
/.
Define the initial set of Euler angles.
./
abgang[0] = 0.01;
abgang[1] = 0.03;
abgang[2] = 0.09;
abgang[3] = -0.001;
abgang[4] = -0.003;
abgang[5] = -0.009;
/.
Compute the equivalent angles and derivatives for a
1-2-3 rotation.
./
eul2xf_c ( abgang, 3, 1, 3, xform );
xf2eul_c ( xform, 1, 2, 3, rpyang, &unique );
if ( unique )
{
printf( "1-2-3 equivalent rotation to input (radians):\n" );
printf( "Roll %12.9f, droll/dt %12.9f\n",
rpyang[0], rpyang[3] );
printf( "Pitch %12.9f, dpitch/dt %12.9f\n",
rpyang[1], rpyang[4] );
printf( "Yaw %12.9f, dyaw/dt %12.9f\n",
rpyang[2], rpyang[5] );
}
else
{
printf( "The values in `rpyang' are not uniquely determined.\n" );
}
return ( 0 );
}
When this program was executed on a Mac/Intel/cc/64-bit
platform, the output was:
1-2-3 equivalent rotation to input (radians):
Roll 0.029998501, droll/dt -0.002999550
Pitch -0.000299950, dpitch/dt 0.000059980
Yaw 0.099995501, dyaw/dt -0.009998650
RestrictionsNone. Literature_ReferencesNone. Author_and_InstitutionN.J. Bachman (JPL) J. Diaz del Rio (ODC Space) W.L. Taber (JPL) E.D. Wright (JPL) Version
-CSPICE Version 2.0.2, 10-AUG-2021 (JDR)
Edited the header to comply with NAIF standard. Added complete
code example based on existing example.
-CSPICE Version 2.0.1, 25-APR-2007 (EDW)
Corrected code in -Examples section, example showed
a xf2eul_c call:
xf2eul_c( xform, 1, 2, 3, rpyang);
The proper form of the call:
xf2eul_c( xform, 1, 2, 3, rpyang, &unique );
-CSPICE Version 2.0.0, 31-OCT-2005 (NJB)
Restriction that second axis must differ from the first
and third was removed.
-CSPICE Version 1.0.1, 03-JUN-2003 (EDW)
Correct typo in Procedure line.
-CSPICE Version 1.0.0, 18-MAY-1999 (WLT) (NJB)
Index_EntriesState transformation from Euler angles and derivatives |
Fri Dec 31 18:41:06 2021