[vtkusers] vtkCellDerivatives

[Andy Bauer]

Hi Martin,

I haven't looked closely enough at vtkTensors (I don't know if I even knew
about it before today) but indeed the ordering output in vtkCellDerivatives
for a velocity vector {u,v,w} needs to be [du/dx, du/dy, du/dz, dv/dx,
dv/dy, ...] like you have it. I'm not sure when vtkTensors is ordered the
way it is.

Cheers,
Andy

On Tue, Jan 19, 2016 at 5:02 PM, Martin Genet <
martin.genet at polytechnique.edu> wrote:

> 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> 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>
>> 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>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>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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