[Insight-users] ReinitializeLevelSetImageFilter

[Karthik Krishnan]

On Fri, Mar 6, 2009 at 9:18 AM, Bryn Lloyd <blloyd at vision.ee.ethz.ch> wrote:

> Hi Karthik,
>
> Thanks for the answer.
>
> The reason why I believe this is the case is that when I pass an image with
> spacings [0.1, 0.1, 0.5]mm I get distance value around 1.0mm, while
> corresponding distance values (from a distance map) are approx. 0.1mm.
>
>
> Actually, now I looked at the code in ReinitializeLevelSetImageFilter.txx.
>
> It does NOT set the OutputSpacing and Origin of the FastMarching object,
> i.e. this must be BUG.


It should. That's a bug then :) Please file a report and it would be great
if could submit a patch if you can.

Thanks
--
karthik


>
> --Bryn
>
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> Karthik Krishnan wrote:
>
>> Bryn:
>>
>> I don't think that is true. The Reinitialize level set filter simply
>> relies on the fast marching filter to generate the signed distance function.
>> The fastmarching filter does take voxel anisotropicity into account when
>> marching the level set front.
>>
>> See the lines involving the update equation in
>> itkFastMarchingImageFilter.h
>>
>>      const int axis = node.GetAxis();
>>      const double spaceFactor = vnl_math_sqr( 1.0 / spacing[axis] );
>>      const double value = double(node.GetValue());
>>      aa += spaceFactor;
>>      bb += value * spaceFactor;
>>      cc += vnl_math_sqr( value ) * spaceFactor;
>>
>>
>> On Fri, Mar 6, 2009 at 8:06 AM, Bryn Lloyd <blloyd at vision.ee.ethz.ch<mailto:
>> blloyd at vision.ee.ethz.ch>> wrote:
>>
>>    Hi all,
>>
>>    Do I understand correctly that the ReinitializeLevelSetImageFilter
>>    does not use the spacing of the input image?
>>
>>    If yes, I guess I need to resample the input image, in order to be
>>    isotropic AND scale the results in order to have Euclidean
>>    distances. Right?
>>
>>    Thanks
>>    Bryn
>>
>>
>>
>>
>>
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>>
>>
>> --
>> Karthik Krishnan
>> R&D Engineer,
>> Kitware Inc.
>> Ph: 518 371 3971 x119
>> Fax: 518 371 3971
>>
>
>
> --
> -------------------------------------------------
> Bryn Lloyd
> Computer Vision Laboratory
> ETH Zürich, Sternwartstrasse 7
> CH - 8092 Zürich, Switzerland
> Tel: +41 44 63 26668
> Fax: +41 44 63 21199
> -------------------------------------------------
>



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