Fwd: Quaternion to axis/angle conversion is buggy when w(4)<0
Vijay Pradeep
vpradeep at willowgarage.com
Wed Dec 10 23:21:43 CST 2008
Below is a patch (generated from [diff -cp]) for the bug listed below:
*** quaternion.m 2008-12-10 21:16:51.000000000 -0800
--- quaternion_ORIGINAL.m 2008-12-10 21:15:28.000000000 -0800
*************** function [a, b, c, d] = quaternion (w, x
*** 54,63 ****
if (abs (norm (w) - 1) > 1e-12)
warning ("quaternion: ||w||=%e, setting=1 for vv, theta", norm(w));
w = w/norm(w);
! endif
! if (w(4)<0)
! w = -w ;
! end
[a, b, c, d] = quaternion (w);
theta = acos (d) * 2;
if (abs (theta) > pi)
--- 54,60 ----
if (abs (norm (w) - 1) > 1e-12)
warning ("quaternion: ||w||=%e, setting=1 for vv, theta", norm(w));
w = w/norm(w);
! endif
[a, b, c, d] = quaternion (w);
theta = acos (d) * 2;
if (abs (theta) > pi)
---------- Forwarded message ----------
From: Vijay Pradeep <vpradeep at willowgarage.com>
Date: Wed, Dec 10, 2008 at 9:13 PM
Subject: Quaternion to axis/angle conversion is buggy when w(4)<0
To: bug at octave.org
Sorry..... the auto bug-reporting tool was having issues. I have
included the bug report below.
Subject: Quaternion to axis/angle conversion is buggy when w(4)<0
-----------
Bug report for Octave 3.0.0 configured for i486-pc-linux-gnu
Description:
-----------
A rotation represented by a quaternion w is equivalently represented
by -w. However, if w(4) is negative,
then the conversion of this quaternion to axis angle is incorrect,
because of the ambiguity in acos(),
which is used in ./octave/3.0.0/m/quaternion/quaternion.m to compute
the rotation angle.
Repeat-By:
---------
w = quaternion([1 0 0], pi/4)
[ax ang] = quaternion( w)
[ax2 ang2] = quaternion(-w)
The rotations represented by [ax ang] and [ax2 ang2] are not equivalent
Fix:
---
in /octave/3.0.0/m/quaternion/quaternion.m
if w(4) is negative, then negate w before operating on it.
Configuration (please do not edit this section):
-----------------------------------------------
uname output: Linux pml 2.6.24-16-generic #1 SMP Thu Apr 10
13:23:42 UTC 2008 i686 GNU/Linux
configure opts: '--host=i486-linux-gnu' '--build=i486-linux-gnu'
'--prefix=/usr' '--datadir=/usr/share' '--libdir=/usr/lib'
'--libexecdir=/usr/lib' '--infodir=/usr/share/info'
'--mandir=/usr/share/man' '--with-blas=-lblas-3gf'
'--with-lapack=-llapackgf-3' '--with-hdf5' '--with-fftw'
'--enable-shared' '--enable-rpath' '--disable-static'
'build_alias=i486-linux-gnu' 'host_alias=i486-linux-gnu' 'CC=gcc'
'CFLAGS=-g -O2' 'LDFLAGS=-Wl,-Bsymbolic-functions' 'CPPFLAGS='
'CXX=g++' 'CXXFLAGS=-g -O2' 'F77=gfortran' 'FFLAGS=-g -O2'
Fortran compiler: gfortran
FFLAGS: -O2
F2C: @F2C@
F2CFLAGS: @F2CFLAGS@
FLIBS: -L/usr/lib/gcc/i486-linux-gnu/4.2.3
-L/usr/lib/gcc/i486-linux-gnu/4.2.3/../../../../lib -L/lib/../lib
-L/usr/lib/../lib -L/usr/lib/gcc/i486-linux-gnu/4.2.3/../../.. -lhdf5
-lz -lgfortranbegin -lgfortran -lm
CPPFLAGS:
INCFLAGS: -I. -I. -I./liboctave -I./src -I./libcruft/misc
C compiler: gcc, version 4.2.3 (Ubuntu 4.2.3-2ubuntu6)
CFLAGS: -O2
CPICFLAG: -fPIC
C++ compiler: g++, version 4.2.3
CXXFLAGS: -O2
CXXPICFLAG: -fPIC
LD_CXX: g++
LDFLAGS:
LIBFLAGS: -L.
RLD_FLAG: -Wl,-rpath -Wl,/usr/lib/octave-3.0.0
BLAS_LIBS: -llapackgf-3 -lblas-3gf
FFTW_LIBS: -lfftw3
LIBS: -lreadline -lncurses -ldl -lhdf5 -lz -lm
LEXLIB:
LIBGLOB:
SED: /bin/sed
DEFS:
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User-preferences (please do not edit this section):
--------------------------------------------------
EDITOR = nano
EXEC_PATH = /usr/lib/octave/3.0.0/site/exec/i486-pc-linux-gnu:/usr/lib/octave/api-v32/site/exec/i486-pc-linux-gnu:/usr/lib/octave/site/exec/i486-pc-linux-gnu:/usr/lib/octave/3.0.0/exec/i486-pc-linux-gnu:/usr/bin:/usr/lib/ccache:/u/vpradeep/ros/ros/bin:~/ros/ros/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
IMAGE_PATH = .:/usr/share/octave/3.0.0/imagelib
PAGER = pager
PS1 = \s:\#>
PS2 = >
PS4 = +
beep_on_error = 0
completion_append_char =
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echo_executing_commands = 0
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gnuplot_command_replot = rep
gnuplot_command_splot = sp
gnuplot_command_title = t
gnuplot_command_using = u
gnuplot_command_with = w
history_file = /u/vpradeep/.octave_hist
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ignore_function_time_stamp = system
info_file = /usr/share/info/octave3.0.info
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makeinfo_program = makeinfo
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string_fill_char =
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suppress_verbose_help_message = 0
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