[vtkusers] vtkCellDerivatives

[Martin Genet]

Thanks Andy.

I need to clarify something: the Derivatives function of vtkCell objects 
returns a derivs vector containing the components of the gradient of 
some vector field defined at the cell nodes; the components are ordered 
in row (as usually in C, i.e., (0,0), (0,1), (0,2), (1,0), (1,1), (1,2), 
(2,0), (2,1), (2,2)). Now in the CellDerivatives filter the derivs 
vector is used to fill a vtkTensors, and then the filter returns the 
internal vector storing the data of the vtkTensors. However, the 
components of the vtkTensors are ordered in column (as usually in 
fortran, i.e., (0,0), (1,0), (2,0), (0,1), (1,1), (2,1), (0,2), (1,2), 
(2,2)). Is it on purpose that the vtkTensors store their data in column 
and not in row? Isn't it a little dangerous to mix both storage in the 
code? Thanks for the clarification!

Martin

On 18/01/2016 13:32, Andy Bauer wrote:
> Hi Martin,
>
> Thanks for following up on this. I found the merge request now and 
> will look at this. In general, developers should request others to do 
> a code review on this. This can be done via something like "@acbauer 
> please review this" or sending an email on this VTK list with a link 
> to the merge request.
>
> Best,
> Andy
>
> On Mon, Jan 18, 2016 at 6:23 AM, Martin Genet 
> <martin.genet at polytechnique.edu 
> <mailto:martin.genet at polytechnique.edu>> wrote:
>
>     Hi Andy,
>
>     I followed the directions, and submitted a patch (19 days ago),
>     but haven't heard anything back.
>
>     In GitLab the merge requests counter is at 0, but when I try to
>     create a new merge request from my commit, it tells the merge
>     request already exists. Is it being reviewed somewhere? Thanks!
>
>     Martin
>
>
>     On 29/12/2015 13:22, Andy Bauer wrote:
>>     Hi Martin,
>>
>>     This patch makes sense. It would need a test if you want to get
>>     your changes into VTK. The directions for contributing to VTK are
>>     at
>>     https://gitlab.kitware.com/vtk/vtk/blob/master/Documentation/dev/git/develop.md.
>>
>>     Cheers,
>>     Andy
>>
>>     On Mon, Dec 28, 2015 at 5:50 PM, Martin Genet
>>     <martin.genet at polytechnique.edu
>>     <mailto:martin.genet at polytechnique.edu>> wrote:
>>
>>         Thanks Andy.
>>
>>         What about simply adding another mode, e.g.
>>         SetTensorModeToComputeGreenLagrangeStrain, to the
>>         vtkCellDerivatives filter? Would the attached patch make sense?
>>
>>         Martin
>>
>>         On 28/12/2015 14:12, Andy Bauer wrote:
>>>         Hi Martin,
>>>
>>>         Changing the name of the SetTensorModeToComputeStrain method
>>>         to something else would break backward compatibility which
>>>         is generally avoided in VTK. Other options for this include
>>>         deriving a class to compute non-linear strain from
>>>         vtkCellDerivatives if it shares enough of the algorithm with
>>>         the linearized version or maybe just creating a new filter.
>>>
>>>         Cheers,
>>>         Andy
>>>
>>>         On Sat, Dec 26, 2015 at 4:36 PM, Martin Genet
>>>         <martin.genet at polytechnique.edu
>>>         <mailto:martin.genet at polytechnique.edu>> wrote:
>>>
>>>             Dear VTK users:
>>>
>>>             I realize that the vtkCellDerivatives filter, when
>>>             SetTensorModeToComputeStrain is activated, returns the
>>>             symmetric part of the gradient of the input vector
>>>             field, which is the linearized strain tensor, i.e., not
>>>             a proper measure of deformation when large displacements
>>>             are involved. Would that make sense to have two
>>>             different modes, SetTensorModeToComputeLinearizedStrain
>>>             or SetTensorModeToComputeSymmetricGradient, and
>>>             SetTensorModeToComputeStrain or
>>>             SetTensorModeToComputeGreenLagrangeStrain? Thanks!
>>>
>>>             Martin
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>>
>>
>
>

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