[MINC-users] xfm2param problem

[EJ Nikelski]

Hi List,

   I have a need to modify xfm files by extracting or retaining various
transform types (transform, rescale, etc). For example, taking an xfm
that transforms to Talairach, but keeping the rescale set to 1.0,
providing me with an xfm that puts my volume into Talaiarch-ish
orientation, while keeping the native brain dimensions (this can be
useful for brain painting). Up until now I've used xfm2param/param2xfm
to modify the xfms as needed -- without a problem.

   However, while working on a new project, I noticed this rather
strange phenomenon.If you create an xfm as follows ...

param2xfm -transform 10 10 10 -rotation 20 20 20 -scale 30 30 30 x0.xfm

... you get as expected. Next, use the individual transformation type
info, and then combine with xfmtool, i.e.,

param2xfm -transform 10 10 10 xT.xfm
param2xfm -rotation 20 20 20 xR.xfm
param2xfm -scale 30 30 30 xS.xfm
xfmtool xT.xfm xR.xfm xS.xfm xTRS.xfm

... "cat xTRS.xfm" shows the 3 appended xfms - OK. But an xfm2param of
the file shows strange translation values ...

jnikelski@[~/xxx]: xfm2param xTRS.xfm
after parameter extraction
-center         0.00000    0.00000    0.00000
-translation  327.16223  309.88623  258.71875
-rotation      20.00000   20.00000   20.00000
-scale         30.00000   30.00000   30.00000
-shear         -0.00000   -0.00000    0.00000


Should this not work? Or am I missing something fundamental here? ..
which is, of course, all too likely :(


Thanks,

-Jim



-- 
E. James Nikelski, Ph.D.
Postdoctoral Research Fellow
Bloomfield Centre for Research in Aging
Lady Davis Institute for Medical Research
Sir Mortimer B. Davis - Jewish General Hospital
McGill University
Tel: (514) 340-8222 x 2298
Fax: (514) 340-8295