[MINC-users] xfmavg and lsq6 transforms

[Vladimir S. FONOV]

So, looks like something is broken in octave, or the way how xfmavg 
reads matrices.

I run standard xfmavg and got result
-center         0.00000    0.00000    0.00000
-translation    0.38288    0.50712    0.52295
-rotation      -0.04862    0.66666   -0.63100
-scale          1.00000    1.00000    1.00000
-shear         -0.00000   -0.00000    0.00000

And then run my SciPy based re-implimentation and got following:
-center         0.00000    0.00000    0.00000
-translation    0.37409    0.75399    0.28905
-rotation     -86.85079    2.70359    1.51978
-scale          1.00000    1.00000    1.00000
-shear          0.00000    0.00000    0.00000



The algorithm is the same as in xfmavg - apply matrix logarithm to all 
transforms, perform element-wise averaging, then apply matrix exponent.


On 16-02-11 11:41 AM, Gabriel A. Devenyi wrote:
> And the average I get, cause I forgot to include it:
>
> MNI Transform File
> %
> % Created by xfmavg with a bit of help from octave
> %    http://www.octave.org/
> %
> % Thu Feb 11 10:47:59 EST 2016>>>> xfmavg scan1_01a0_GenericAffine.xfm
> scan1_02a0_GenericAffine.xfm scan1_02b0_GenericAffine.xfm
> scan1_03a0_GenericAffine.xfm scan1_04a0_GenericAffine.xfm
> scan1_05a0_GenericAffine.xfm scan1_05b0_GenericAffine.xfm
> scan1_06a0_GenericAffine.xfm scan1_07a0_GenericAffine.xfm
> scan1_07b0_GenericAffine.xfm scan1_08b0_GenericAffine.xfm
> scan1_10b0_GenericAffine.xfm scan1_11b0_GenericAffine.xfm
> scan1_12a0_GenericAffine.xfm scan1_13a0_GenericAffine.xfm
> scan1_14a0_GenericAffine.xfm scan1_14b0_GenericAffine.xfm
> scan1_16b0_GenericAffine.xfm scan2_01a0_GenericAffine.xfm
> scan2_01b0_GenericAffine.xfm scan2_02a0_GenericAffine.xfm
> scan2_03a0_GenericAffine.xfm scan2_06a0_GenericAffine.xfm
> scan2_06b0_GenericAffine.xfm scan2_08a0_GenericAffine.xfm
> scan2_09a0_GenericAffine.xfm scan2_11a0_GenericAffine.xfm
> scan3_02a0_GenericAffine.xfm scan3_03a0_GenericAffine.xfm
> scan3_07a0_GenericAffine.xfm scan3_09a0_GenericAffine.xfm
> scan3_09b0_GenericAffine.xfm average/average.xfm
>
> Transform_Type = Linear;
> Linear_Transform =
>   9.99871671e-01 1.10030065e-02 1.16437239e-02 3.82880856e-01
>   -1.10121374e-02 9.99939105e-01 7.20365393e-04 5.07116829e-01
>   -1.16350887e-02 -8.48495237e-04 9.99931950e-01 5.22949707e-01;
>
> ​
>


-- 
Best regards,

  Vladimir S. FONOV ~ vladimir.fonov <at> gmail.com