[Insight-users] VectorImage Orientation from NRRD

[Karthik Krishnan]

Luis Ibanez wrote:
>
> Hi Karthk, Gordon,
>
>
> This problem has been solved since September 13th 2008.
>
>
> Simply turn on the CMake flag:
>
>
>           ITK_IMAGE_BEHAVES_AS_ORIENTED_IMAGE
>
>
> That will make the itk::Image behave like the itk::OrientedImage.
>
>
> Since the itk::VectorImage derives from the itk::Image, 
It derives from itk::ImageBase. If I recall correctly, at that time, 
deriving
from itk::Image required me to make certain methods like
TransfromPhyscalPointToContinuousIndex virtual. Same reason why
OrientedImage derives from ImageBase and not Image.

Thanks
--
karthik
> then
> the correct behavior will also be inherited.
>
>
>    Thanks
>
>
>       Luis
>
>
>
> -------------------------
> Karthik Krishnan wrote:
>> Dan, Gordon:
>>
>> As you've already realized Dan, itk::VectorImage provides no more 
>> (and no less)
>> support for direction cosines than itk::Image. They simply ignore it 
>> and do not,
>> unlike itk::OrientedImage, take it into account when translating 
>> indices into
>> world coordinates, or use it when computing derivatives on images.
>>
>> NRRD, I believe, allows for encoding both the patient coordinate system
>> (represented by space_origin and space_directions) and additional
>> coordinate systems pertinent to DWI images (gradient coil's directions).
>> Whatever direction cosines it will set on itk::Image or 
>> itk::VectorImage are
>> ignored.
>>
>> In retrospect, I mistakenly derived VectorImage from ImageBase, rather
>> than OrientedImage, but both classes came out the same year, when
>> OrientedImage was still in its infancy with a CVS log stating
>> "It may be removed be before the next release".
>>
>> As a solution, the VectorImage class could quite easily be made to
>> take into account of the direction cosines exactly as OrientedImage 
>> does,
>> by just copying the methods over from OrientedImage. Perhaps that
>> could be on the list of things ToDo whenever the next lengthy
>> discussion on Orientation comes up in ITK. I think we have one
>> every month. :)
>>
>> Thanks
>>

-- 
Karthik Krishnan
R & D Engineer,
Kitware Inc,
Ph:  518 371 3971 x119
Fax: 518 371 3971