Dear Dr. Ashburner,
Thanks for your email. I did have my reservations when putting this
analogy down, but still did it anyhow... What I meant by using the
"letter b" analogy was to have the round part of the "b" represent the
temporal, parietal and occipital lobes, and have the top part of the
"b" represent the frontal lobe, when the brain is in a sagittal view
across its midline. So, it is as if you're looking sideways at a brain
of someone who is lying down and looking up. Flipping it 90 degrees
clockwise would mean having the person stand up ("b" becomes "sigma")
and the last 180 degrees flip would require him/her to turn to the
opposite side. I hope this makes sense now.
Thanks a lot,
Susana
On Nov 16, 2004, at 5:36 AM, John Ashburner wrote:
>
> I have to admit that I am struggling a little bit with the analogy.
> The order
> of operations matters when combining rotations together, and the order
> that
> it is done is SPM is to do yaw, pitch and roll in that order. Zooms
> are also
> done before rotations, so maybe it would help to think about flipping
> (a zoom
> of -1) before rotating. Also, ensure that the flipping is really
> necessary.
> Maybe you really need a 180 degree (pi radians) rotation instead.
>
> Best regards,
> -John
>
>> I have an fMRI image that needs to be rotated by 90 degrees in one
>> direction and then flipped 180 degrees along another axis.
>>
>> Let me try to describe the situation: When I display the image, the
>> brain
>> in the sagittal view looks like the letter 'b'. I should turn it 90
>> degrees
>> clockwise, to make it look like a "sigma" and then flip it along a
>> vertical
>> line (to have it look like a "sigma" facing left). (Apologies for the
>> silly
>> analogy.)
>>
>> I have tried the pitch, yaw and roll options but haven't managed to
>> put the
>> image in the direction it should be. When one direction is finally
>> ok, at
>> least one other becomes wrong again... Could anyone please help me
>> out with
>> this?
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