Hi,
in case you don't want to code you can always try calculating the
angle via the series expansion of the arctan(x) for |x| < 1...
just a though...
christian
On 16 Jul 2007, at 19:34, Saad Jbabdi wrote:
> In that case, I don't know!
>
> make_dyadic_vectors is useful to extract the mean fibre orientation
> from bedpost samples. As it calculates sines and cosines for you, I
> thought it might be a good hack for extracting sines and cosines
> from images! But if you need arctan, then I don't know any fsl tool
> that does calculate that. You will need to code it yourself! (note
> that it is not difficult to add functionalities to avwmaths).
>
> cheers,
> saad
>
>
> On 16 Jul 2007, at 19:19, Jason Steffener wrote:
>
>> Dear Saad,
>> Hello. Thank you for the feedback.
>> I am actually looking for the arctan to calculate the angles.
>> And what is make_dyadic_vectors used for? And how can I find out
>> more about how this function works?
>>
>> Thank you,
>> Jason.
>>
>>
>> ----- Original Message ----
>> From: Saad Jbabdi <[log in to unmask]>
>> To: [log in to unmask]
>> Sent: Monday, July 16, 2007 1:38:17 PM
>> Subject: Re: [FSL] Arc Tangent of images
>>
>> Hi Jason -
>>
>> Calculating the tangent of an angle (in radian) using fsl tools is
>> straightforward if you take advantage of make_dyadic_vectors.
>> all you need to do is provide two images:
>>
>> make_dyadic_vectors image1 image2 output
>> where image2 is all zeros and image1 are your angles x.
>>
>> then the ouput is a 4D image where the 4th dimension has the
>> following entrie: [sin(x)cos(0); sin(x)sin(0); cos(x)]
>>
>> then you divide the 1st by the last entry to get the tangent!
>>
>> for the arctangent, it is a little bit trickier... but i'm not
>> sure which one you really want given your email?
>>
>>
>> i hope this is helpful...
>> saad
>>
>>
>> On 16 Jul 2007, at 16:12, Jason Steffener wrote:
>>
>>> Hello all,
>>>
>>> Is there any way of taking the arc tan (or sine/cosine) of two
>>> images in FSL? I can easily do it in MatLab but am trying to set
>>> up a "pure" FSL analysis.
>>>
>>> Thank you,
>>> Jason.
>>
>> ---------------------------------------------------------------------
>> ------
>> Saad Jbabdi,
>> Postdoctoral Research Assistant,
>> Oxford University FMRIB Centre
>>
>> FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
>> +44 (0) 1865 222545 (fax 222717)
>> [log in to unmask] http://www.fmrib.ox.ac.uk/~saad
>> ---------------------------------------------------------------------
>> ------
>>
>>
>>
>>
>>
>>
>
> ----------------------------------------------------------------------
> -----
> Saad Jbabdi,
> Postdoctoral Research Assistant,
> Oxford University FMRIB Centre
>
> FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
> +44 (0) 1865 222545 (fax 222717)
> [log in to unmask] http://www.fmrib.ox.ac.uk/~saad
> ----------------------------------------------------------------------
> -----
>
>
>
>
____
Christian F. Beckmann
University Research Lecturer
Oxford University Centre for Functional MRI of the Brain (FMRIB)
John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK.
[log in to unmask] http://www.fmrib.ox.ac.uk/~beckmann
tel: +44 1865 222551 fax: +44 1865 222717
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