[MINC-users] CIVET-1.1.12 and sqrt(2) offset

[Claude LEPAGE]

Hi,

You have to multiply by sqrt(2) to obtain the correct fwhm in 
CIVET-1.1.12 for surface blurring.

-thickness tlink fwhm_desired*sqrt(2)
-area-fwhm fwhm_desired*sqrt(2)
-volume-fwhm fwhm_desired*sqrt(2)

For example, if you want fwhm=20mm, you have to specify
20*sqrt(2)=28.28. However, since fwhm is used in the 
filename for the thickness files, I suggest to round 
fwhm if you don't want filenames with a dot in them. 

If you used a value of 30mm before, then this corresponds
to an effective fwhm of 30/sqrt(2)=21.21mm. 

Sorry for the inconvenience.

Claude


>
> Hi all,
>
> I was previously aware that CIVET-1.1.12 has a sqrt(2) mistake according to
> the CIVET-2.0 changelog: "corrected fwhm for surface smoothing (was off by
> sqrt(2) in 1.1.12)"
>
> Is the "fwhw for surface smoothing" one of the command-line parameters that
> could be adjusted to compensate? (my only guess is is "-area-fwhm <fwhm>")
> If so, is it bigger or smaller by sqrt(2)?
>
> Thanks!
>
> -- 
> Gabriel A. Devenyi B.Eng. Ph.D.
> Research Computing Associate
> Computational Brain Anatomy Laboratory
> Cerebral Imaging Center
> Douglas Mental Health University Institute
> McGill University
> t: 514.761.6131x4781
> e: gdevenyi at gmail.com
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