thanks a lot
-L
On May 24, 2004, at 6:28 PM, Mark Jenkinson wrote:
> Hi,
>
>> Amatrix = load ('original2standard')
>> xyz2 = Amatrix * [ x y z 0]'
>>
>> The actual questions:
>> 1) Should the xyz2 coordinates should be the coordinates for the same
>> structure after the transformation (ie- registered.img)?
>
> Yes, that's right.
>
>> 2) is the frame of reference for that rotation the same as the one in
>> the reference image, the original image (ie- origin, voxel sizes...),
>> or is it relative to the first voxel in the file?
>
> The coordinates are all in mm, not voxels, with 0,0,0 located at the
> voxel in the lower-left corner of the image (that is, the first voxel
> in
> the img file) So, to get mm coordinates from voxel coordinates, just
> multiply by the appropriate voxel dimensions (in mm).
>
>> 3) I should also be able to invert the transformation matrix and go
>> back and forth between the spaces, no?
>
> Yep, as everything is in mm, all you need to do is invert the matrix.
>
>> 4) Do all these things hold true in the case of 12DOF transformations?
>> I'm thinking they should ...
>
> Yes, it holds for all DOF.
>
>> 5) what is the .xfm file for?
>
> They are MEDx transforms (for historical reasons...)
>
>> I'm sorry if this is a newbie question...I've been trying to test
>> these
>> questions on a synthetic image made up of a few dots but I'm getting
>> weird results. Maybe I'm using the functions wrong ...
>
> Your problems are probably to do with your choice of coordinate
> unit (mm vs voxels) and coordinate centre/origin. Once these are
> consistent things should work OK.
>
> All the best,
> Mark
>
>
>
>
>> thanks a lot
>>
>> -Luis
>>
>>
>>
>>
>> --
>> ( http://www.eecs.umich.edu/~hernan )
>
>
--
( http://www.eecs.umich.edu/~hernan )
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