[ITK] [ITK-dev] image and deformation field physical space check

[Matt McCormick]

Hi Brian,

Thanks for discussing this.

I think a combination of fixing the underlying issue that is being
brought up by the exception, relaxing the tolerance, and improving the
documentation is a good approach.

2 cents,
Matt

On Mon, Nov 3, 2014 at 11:40 AM, brian avants <stnava at gmail.com> wrote:
> This email is motivated by this issue:
>
> https://github.com/stnava/ANTs/issues/74
>
> but it is not isolated to ants.   Worth a read for additional context.
>
> ITK currently enforces a relatively strict check that image and displacement
> fields "occupy the same physical space."  However, for some unclear (to me)
> reasons, the direction matrices or origins of images can lose precision when
> passing through ITK pipelines ( especially through resampling or
> resolution-changing filters ).  This results in filters aborting and this
> can occur at various different places in a complex series of ITK-based
> operations.
>
> My concern with this is that it can lead to a very severe loss of
> productivity when this somewhat unpredictable error occurs.   For instance,
> a user downloads a toolkit based on ITK ( itk-snap, ants, elastic,
> brainsfit, joint label fusion, etc).   The user expects registration or
> segmentation filters to "work well" especially when the data is of a
> standard sort.   Then, after some oft-substantial execution time, this
> mysterious error appears:
>
> itk::ERROR: ImageToImageFilter(0x7fb3b2307ac0): Inputs do not occupy the
> same physical space!
>
>
> While I am all for correctness, when the impact on productivity exceeds a
> certain threshold, I think it is useful to bend the rules a bit.   Perhaps
> one of these would improve the situation:
>
> 1)    change:
>
> ITKv4/Modules/Filtering/DisplacementField/include/itkDisplacementFieldTransform.hxx
>
> and
>
> ITKv4/Modules/Core/Common/include/itkImageToImageFilter.hxx
>
> changing direction tolerance and coordinate tolerance to 1.e-4
>
> https://github.com/InsightSoftwareConsortium/ITK/blob/master/Modules/Filtering/DisplacementField/include/itkDisplacementFieldTransform.hxx#L454-L457
>
> https://github.com/InsightSoftwareConsortium/ITK/blob/master/Modules/Core/Common/include/itkImageToImageFilter.hxx#L40-L41
>
> and change the documentation too:
>
> https://github.com/InsightSoftwareConsortium/ITK/blob/master/Modules/Core/Common/include/itkImageToImageFilter.h#L76-L87
>
> 2)  Change the exception to a warning.  This would at least allow complex
> pipelines to execute while notifying the user of a possible issue.
>
> 3)  Document all of the places that the user/developer should call:
>
> Set/GetCoordinateTolerance  Set/GetDirectionTolerance  .
>
> This last solution would require adding Set/GetCoordinate and Direction
> tolerance to:
>
> https://github.com/InsightSoftwareConsortium/ITK/blob/master/Modules/Filtering/DisplacementField/include/itkDisplacementFieldTransform.h
>
> as well, for consistency.
>
> Anyway, I raise this issue b/c of the many man and computer hours lost by
> this check.
>
> Not once has this check actually helped us, in any measurable way, avoid
> errors.
>
>
>
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