[Paraview] trying to achieve odd symmetry reflection where axis is inside original domain

[Noah Reddell]

Hi Cory,

   Thanks for your interest.  I can answer your two questions pretty
compactly.

*> Could you describe the glitches? I couldn't understand them from just
the images you attached.*
The scalar variable EM_field_n_c4 in the referenced .VTS file is the
analytic function: *tanh(-x/4.082)*.
The resulting odd symmetry reflection about x=0 should achieve the same
function.  The function is smooth.
I suspect the glitches come from the two nodes left of x=0 in my original
data.  I speculate that the Reflect filter is reflecting those as well.
Actually, I'm pretty sure I observed as much yesterday when not using the
option to copy the original data.  This means some kind of funny overlap
occurs between the before and after reflection data.

*> what do you expect to see at x=0 if your original data doesn't have
anything at x = 0?*
My preference would be to have no new nodes created along x=0.  I have
nodes at x= { 0-d2,  0-d1,  0+d1, 0+d2, 0+d3, 0+d4, ... }.
One way to look at the problem would be to reflect nodes {0+d3,0+d4,...}
about x=0 because the the existing two nodes {0-d2, 0-d1} are already
correct.
Another way to look it it is to discard existing nodes {0-d2, 0-d1} and
reflect what remains about x=0.
In both cases, reflect with possible negative scaling!
I don't care if a new node is created at x=0 which would be the average
value of nodes {0-d1, 0+d1}.  But Paraview linear interpolation already
does this for presentation purposes and it would not be strictly correct
for the underlying polynomial element.

Best Regards,

Noah Reddell

On Mon, Nov 2, 2015 at 7:42 AM, Cory Quammen <cory.quammen at kitware.com>
wrote:

> Hi Noah,
>
> See answers and questions for you inlined below.
>
>
>> 1)  My original data extends beyond the x=0 symmetry plane by two data
>> points.  And I have no data point on x=0 itself.  This is because in the
>> simulation, there is a third-order polynomial element centered on x=0.
>>
>
> What would you like to see on x=0?
>
>
>> 2)  My data is represented as Structured Curvilinear Grid (.VTS files)
>> though in actuality, it is rectilinear.
>>
>
> Shouldn't be a problem.
>
>
>> 3)  Some data arrays have odd symmetry, such that f(x<0) = -f(x>0)
>>
>
> The Reflect filter doesn't support this, but you obviously know that.
>
>
>> Here’s what I’ve tried.
>> A) Use the Reflect filter, reflect about x=0.  Works quite well for even
>> symmetry data, but the odd-symmetry data is misrepresented with opposite
>> sign for (x<0).  Also, there are glitches with the doubled-up mesh points
>> about x=0.  That becomes obvious when I tried to add a calculator to
>> correct the odd symmetry based on (x<0) boolean expression.
>>
>
> Could you describe the glitches? I couldn't understand them from just the
> images you attached.
>
>
>> B) Manually select data points with (x>0); Extract Selection; Reflect
>> that extraction; Group original and new selection.  Problem:  I end up with
>> a band of missing data for the cell centered on x=0.
>>
>
> Again, what do you expect to see at x=0 if your original data doesn't have
> anything at x = 0?
>
> Thanks,
> Cory
>
>
>> Ideally, I want to end up with a consistent full-domain representation
>> such that I can perform stream line traces across the x=0 mid-plane.
>>
>> I’d be very grateful if anyone could point out a working solution.
>> Here’s one of my data files and some screenshots of my failed attempts.  (
>> The scalar data item EM_field_n_c4 is a good odd-symmetry example. )
>>
>> VTS data file 800 kB
>> <https://dl.dropboxusercontent.com/u/54478577/supporting%20forum%20posts/paraview_odd_symmetry_help/harris_current_sheet_equilibreum_2.vts>
>>
>> Existing Curvilinear Mesh representation
>> <https://dl.dropboxusercontent.com/u/54478577/supporting%20forum%20posts/paraview_odd_symmetry_help/By.jpg>
>>
>> ProblemA demonstration of missing band about x=0
>> <https://dl.dropboxusercontent.com/u/54478577/supporting%20forum%20posts/paraview_odd_symmetry_help/missingband.jpg>
>>
>> ProblemB demonstration of glitch at centerline
>> <https://dl.dropboxusercontent.com/u/54478577/supporting%20forum%20posts/paraview_odd_symmetry_help/glitch_at_centerline.jpg>
>>
>>
>> Best Regards,
>>
>> Noah Reddell
>> University of Washington
>>
>>
>> _______________________________________________
>> Powered by www.kitware.com
>>
>> Visit other Kitware open-source projects at
>> http://www.kitware.com/opensource/opensource.html
>>
>> Please keep messages on-topic and check the ParaView Wiki at:
>> http://paraview.org/Wiki/ParaView
>>
>> Search the list archives at: http://markmail.org/search/?q=ParaView
>>
>> Follow this link to subscribe/unsubscribe:
>> http://public.kitware.com/mailman/listinfo/paraview
>>
>>
>
>
> --
> Cory Quammen
> R&D Engineer
> Kitware, Inc.
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://public.kitware.com/pipermail/paraview/attachments/20151102/6e18fcaf/attachment.html>