[vtkusers] vtkCellDerivatives

[Martin Genet]

Thanks Andy.

Well, I might be wrong but I'm under the impression that 
vtkCellDerivatives returns [du/dx, dv/dx, dw/dx, du/dy, dv/dy, ...]. Am 
I wrong?

Martin

On 20/01/2016 03:07, Andy Bauer wrote:
> 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 
> <mailto: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
>>     <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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