[Insight-developers] itkOrientedImage type definition

[Kent Williams]

Gordon (and others): I am working on the nifti ImageIO right now. 
There's a version right now, that will be included in the next 
checkpoint release, that just supports reading NIFTI files and doesn't 
consider orientation at all.

After the checkpoint release, I'll be checking in a version that A) both 
reads and writes and B) handles embedded orientation information.

The 'gold standard' of orientation in ITK is (and will be) the DICOM 
direction cosines.  In other words, the direction cosines in 
itk::ImageBase will be either A) the image file format's native 
orientation information converted to Dicom Direction Cosines or B) 
'Identity' direction cosines, with no indication of anatomical orientation.

An open issue would be how to determine if the Direction Cosines just 
happen to correspond to Identity, or if no orientation information is 
given.  In Dicom terms, identity would correspond to Transverse scan, 
with dimensions (fastest moving to slowest)  Patient right to left, 
anterior to posterior, inferior to superior.

Presumably, once the orientation issues get settled in Insight, any 
remaining ambiguity can be addressed by the client application -- one 
presumes any specific applications could make some simplifying 
assumptions about the input data.



Gordon Kindlmann wrote:

>
> If the orientation information came from Analyze or NIFTI, is it  
> converted to LPS?
>
> Gordon
>
> On Aug 18, 2005, at 4:08 PM, Lorensen, William E (Research) wrote:
>
>> I believe that the direction cosines in ITK are always in LPS. I  
>> just copy in the dicom direction cosines.
>>
>> Bill
>>
>> -----Original Message-----
>> From: insight-developers-bounces+lorensen=crd.ge.com at itk.org
>> [mailto:insight-developers-bounces+lorensen=crd.ge.com at itk.org]On  
>> Behalf
>> Of Simon Warfield
>> Sent: Thursday, August 18, 2005 3:01 PM
>> To: insight-users at itk.org; insight-developers at itk.org
>> Subject: [Insight-developers] itkOrientedImage type definition
>>
>>
>>
>> I am looking at the documentation that describes directions here:
>> http://www.itk.org/Doxygen/html/classitk_1_1Image.html#w14
>>
>> This indicates that there is the possibility to represent a matrix of
>> direction cosines.
>> Direction cosines represent the angle between two sets of basis  
>> vectors.
>> http://mathworld.wolfram.com/DirectionCosine.html
>>
>> In order to understand what the orientation of an itkOrientedImage is,
>> there must be some way to specify or to record what those basis  
>> vectors are.
>> For example, the definition of DICOM direction cosines warrants that
>> what is being provided is the angle between the patients anatomy in  
>> what
>> is referred to as the Left-Posterior-Superior orientation and the  image
>> columns and rows.
>>
>>   With respect to what are the ITK direction cosines computed ?  If it
>> is not specified then the orientation of an image containing such
>> direction cosines is still unknown, which would defeat the purpose of
>> providing an orientation.
>>
>> -- 
>> Simon
>>
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>
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