[Insight-developers] [GDCM] ITK Origin and coordinate system

[Lorensen, William E (GE, Research)]

My interpretation is the same as Leila's. I read that the origin is always in LPS. I think it needs to be transformed into the ITK coordinate farem.


-----Original Message-----
From: Leila baghdadi [mailto:baghdadi at sickkids.ca]
Sent: Tuesday, January 17, 2006 1:29 PM
To: Mathieu Malaterre
Cc: insight-developers at itk.org; Gordon Kindlmann; Lorensen, William E
(GE, Research); Vince Magnotta
Subject: Re: [Insight-developers] [GDCM] ITK Origin and coordinate
system


Hey petit frere,

I think you are right about the origin being a fixed point, i.e, for the
header information,
but once you apply the direction cosines to the image (i.e, right before
visualization), shouldn't the origin be resampled as well?

Leila

On Tue, 2006-01-17 at 13:08 -0500, Mathieu Malaterre wrote:
> Bill,
> 
> 	We are having a discussion with Gordon about a problem regarding the 
> Origin of an itkImage read from a DICOM file. A while ago you put this 
> code into itkGDCMImageIO(*). After discussion with Luis we came to the 
> conclusion that the Origin is a fixed point. If you want to compute a 
> point then yes you need to use the direction cosine and refer to the 
> origin. But the origin should not change, right ?
> 
> Comments welcome,
> Mathieu
> 
> 
> (*)
>    // DICOM specifies its origin in LPS coordinate, regardless of how
>    // the data is acquired. itk's origin must be in the same
>    // coordinate system as the data. This code transforms the DICOM
>    // origin into the itk origin. The itk origin is computed by
>    // multiplying the inverse(transpose) of the direction cosine times
>    // the dicom origin.
>    vnl_vector<double> itkOrigin(3), dicomOrigin(3);
>    vnl_matrix<double> dicomDirection(3,3);
>    dicomOrigin[0] = header.GetXOrigin();
>    dicomOrigin[1] = header.GetYOrigin();
>    dicomOrigin[2] = header.GetZOrigin();
>    for (unsigned int ii = 0; ii < 3; ii++)
>      {
>      dicomDirection[0][ii] = rowDirection[ii];
>      dicomDirection[1][ii] = columnDirection[ii];
>      dicomDirection[2][ii] = sliceDirection[ii];
>      }
>    itkOrigin = dicomDirection * dicomOrigin;
>    m_Origin[0] = itkOrigin[0];
>    m_Origin[1] = itkOrigin[1];
>    m_Origin[2] = itkOrigin[2];
> _______________________________________________
> Insight-developers mailing list
> Insight-developers at itk.org
> http://www.itk.org/mailman/listinfo/insight-developers
-- 
Leila baghdadi <baghdadi at sickkids.ca>