[ITK] Redudancy in LevelSetBase hierarchy

[Matt McCormick]

Hi David,

Arnaud and Kishore are LevelSetsv4 experts, although they may or may
not have time to work on the code further.  If patches are submitted
to Gerrit for review, please add them as reviewers so they have an
opportunity to review the changes.

Thanks,
Matt

On Wed, Jun 22, 2016 at 10:57 AM, David S. Paik (Elucid Bioimaging)
<david.paik at elucidbio.com> wrote:
> Dženan,
>
>   Thank you for your response!  Although it really is more the level set
> segmentation framework for V4 that this applies to.  If either of you can
> point me to someone who’s done work on that, it’d be appreciated.
>
> Thanks!
> David
>
>
> On Jun 22, 2016, at 3:30 AM, Dženan Zukić <dzenanz at gmail.com> wrote:
>
> Hans, I think you were involved with refactoring registration framework for
> V4. Can you pitch in?
>
> Regards
>
> On Sat, Jun 11, 2016 at 1:24 AM, David S. Paik (Elucid Bioimaging)
> <david.paik at elucidbio.com> wrote:
>>
>> I am going through the level set v4 classes in 4.9.1 and I noticed a few
>> things.
>>
>> In itk::LevelSetBase
>>
>> -  EvaluateMeanCurvature( const InputType& iP ) is declared pure virtual
>> (.h line 75) but a definition is provided (.hxx line 88).  While
>> syntactically permissible, this seems more likely an oversight rather than
>> an intentional design. (see below)
>>
>> - Both versions of EvaluateLaplacian are pure virtual even though they
>> could be computed at this point in the hierarchy as the trace of the Hessian
>> matrix.  This is analogous to how EvaluateGradientNorm is calculated even
>> though EvaluateGradient is still pure virtual in this class. (see below)
>>
>>
>> In itk::DiscreteLevelSetImage
>>
>> - EvaluateLaplacian (both versions) do their own redundant calculation of
>> second derivatives even though they may have already been calculated in the
>> Hessian matrix.  There’s probably a design tradeoff between redundantly
>> computing the Laplacian (as it is now) vs. Laplacian triggering a full
>> Hessian computation even if the off diagonal elements of the Hessian are not
>> used.  One possibility is to check to see if Hessian has been computed and
>> if so use it but not trigger a full Hessian computation.
>>
>> - EvaluateMeanCurvature (both versions) override itk::LevelSetBase’s
>> version but they appear to be exactly the same.  The virtual function calls
>> should work from the base class.  Not a bug but this seems to be an
>> unnecessary redundancy.  Am I missing something?
>>
>>
>> David
>>
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>
>
>
>
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