[Paraview] [EXT] Re: How to find the nearest quad element?

[Marco Nawijn]

"for the cell locator." -> OOPS: I mean for the point locator of course.

Marco


On Wed, Sep 9, 2015 at 2:49 PM, Marco Nawijn <nawijn at gmail.com> wrote:

> Hi Dennis,
>
> Sorry for not coming back with an example yet. I had a few other things
> that keep
> me really busy. I don't have a solution yet, but I was wondering if you
> visualized
> the center point locations you believe are used as a basis for the cell
> locator.
> I typically do this by creating a vertex (point cell) for every point that
> I am interested
> in. In this way you can plot the point, the hex and the quad and continue
> debugging
> from there.
>
> Marco
>
>
> On Wed, Sep 9, 2015 at 2:16 PM, Dennis Conklin <
> dennis_conklin at goodyear.com> wrote:
>
>> All,
>>
>>
>>
>> I thought an example of my “not sensible” output would make this clearer,
>> see the picture below.
>>
>> All of the highlighted hex elements are at the edge of the piece and the
>> lower edge of the piece is covered in membrane elements (quads).   So, each
>> of the highlighted hex elements actually shares 4 nodes with a quad.
>> Therefore, the closest quad to each of those hex elements should be the
>> attached quad, and each of the highlighted hexes should get a different
>> index returned from FindClosestPoint.
>>
>> I have displayed the actual index returned from FindClosestPoint on each
>> hex.    So there are 5 hexes that FindClosestPoint thinks quad18 is the
>> closest quad, similarly 5 hexes for quad19, 5 hexes for quad20.
>>
>>
>>
>> I expect that each of the highlighted hexes should get a different index
>> returned from FindClosestPoint and that index should correspond to the
>> individual membrane that each hex shares 4 nodes with.
>>
>>
>>
>> I still am not sure that this will make sense, but any ideas why this is
>> not behaving as I expected?
>>
>>
>>
>> Thanks for any help
>>
>>
>>
>> Dennis
>>
>>
>>
>>
>>
>> *From:* Dennis Conklin
>> *Sent:* Tuesday, September 08, 2015 2:54 PM
>> *To:* 'Marco Nawijn'
>> *Cc:* Paraview (paraview at paraview.org)
>> *Subject:* RE: [EXT] Re: [Paraview] How to find the nearest quad element?
>>
>>
>>
>> All,
>>
>>
>>
>> So I have taken a shot at this and have a few questions.
>>
>>
>>
>> I have multiple blocks of quads and I need to find the nearest quad for
>> every hex in the model (also multiple blocks).  The purpose of this is to
>> assign the Normal to the nearest quad to each hex
>>
>>
>>
>> My approach was:
>>
>> 1.       Create 2 inputs for the Programmable Filter
>>
>> a.      1st is regular Exodus file
>>
>> b.      2nd is regular file with Extract Surface/Generate Surface
>> Normals/Cell Centers filters run – this has no cells, only points at the
>> quad centers that contain what I want, which is Normals to the quad (also
>> contains points at the hex centers, which I will use later)
>>
>> 2.      In PF, I loop thru all quad blocks in the 2nd input and build 2
>> arrays.  First array has all the points in all the quad blocks in the 2nd
>> input, and the second array has the corresponding normal associated with
>> those points.
>>
>>
>>
>> Now, I make a vtk.vtkKdTree and use BuildLocatorFromPoints(my pt array)
>>
>> Now I loop over all hex in model, call FindClosestPoint using the point
>> from the Cell Centers filter for the hex.  This returns an integer index
>> and I assume Normals(index) is the normal associated with that quad
>>
>>
>>
>> I do not get a sensible output.
>>
>>
>>
>> My conclusion is that when I go thru this process, the index returned
>> from FindClosestPoint is no longer synced to the original order of the
>> points, which causes it to be a bad index into my Normals array.
>>
>>
>>
>> It’s also extremely possible that there is some setup of kdTree that I
>> need to do first that I am omitting.
>>
>>
>>
>> So, is there a way to get kdTree to preserve the original order of the
>> points, or is there another way to get an index back into my array of
>> Normals, such that I can figure out which one is associated with the return
>> from FindClosestPoint
>>
>>
>>
>> I’m not sure this is clear enough to be interpreted by anyone, but here’s
>> hoping.
>>
>>
>>
>> Dennis
>>
>>
>>
>> *From:* Marco Nawijn [mailto:nawijn at gmail.com <nawijn at gmail.com>]
>> *Sent:* Tuesday, August 25, 2015 11:26 AM
>>
>> *To:* Dennis Conklin
>> *Cc:* Paraview (paraview at paraview.org)
>> *Subject:* Re: [EXT] Re: [Paraview] How to find the nearest quad element?
>>
>>
>>
>> Hi Dennis,
>>
>>
>>
>> That timeframe is ok for me.
>>
>>
>>
>> Marco
>>
>>
>>
>>
>>
>> On Tue, Aug 25, 2015 at 5:24 PM, Dennis Conklin <
>> dennis_conklin at goodyear.com> wrote:
>>
>> Marco,
>>
>>
>>
>> I am actually tied up for the next week or so, so if you can post a
>> sample in that timeframe that would be perfect.
>>
>>
>>
>> Thanks very much
>>
>>
>>
>> Dennis
>>
>>
>>
>> *From:* Marco Nawijn [mailto:nawijn at gmail.com]
>> *Sent:* Tuesday, August 25, 2015 11:21 AM
>> *To:* Dennis Conklin
>> *Cc:* Paraview (paraview at paraview.org)
>> *Subject:* Re: [EXT] Re: [Paraview] How to find the nearest quad element?
>>
>>
>>
>> Hi Dennis,
>>
>>
>>
>> You might also be interested in the vtkCellCenters filter. As the name
>> suggests, it
>>
>> will generate the centers of the cells for you. If you are not in a big
>> rush, I can build
>>
>> you a small self contained sample in Python that demonstrates the filter
>> and the
>>
>> use of the point locator. I am a little busy at the moment, but I can
>> post the sample
>>
>> in a couple of days.
>>
>>
>>
>> Marco
>>
>>
>>
>>
>>
>> On Tue, Aug 25, 2015 at 1:40 PM, Dennis Conklin <
>> dennis_conklin at goodyear.com> wrote:
>>
>> Marco,
>>
>>
>>
>> Thanks for that tip – I’m not very familiar with vtk and I’ve never heard
>> of that class but it seems appropriate so I will try to dig into it.
>>
>>
>>
>> Thanks again
>>
>>
>>
>> Dennis
>>
>>
>>
>> *From:* Marco Nawijn [mailto:nawijn at gmail.com]
>> *Sent:* Monday, August 24, 2015 10:28 AM
>> *To:* Dennis Conklin
>> *Cc:* Paraview (paraview at paraview.org)
>> *Subject:* [EXT] Re: [Paraview] How to find the nearest quad element?
>>
>>
>>
>> What about the following:
>>
>>
>>
>> Generate two additional datasets, one containing (an approximate of) the
>> center of the hex elements, the second the center of the quads. Then create
>> a vtkKdTreePointLocator object based on the center points of the quad
>> elements. Than loop over the centers of the hex elements and use one of the
>> Find* methods to get the closest quad.
>>
>>
>>
>> Marco
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> On Fri, Aug 21, 2015 at 2:21 PM, Dennis Conklin <
>> dennis_conklin at goodyear.com> wrote:
>>
>> Sam,
>>
>> Thanks for responding.  You have helped me several times in the past and
>> I am always grateful for your insights.  In this case there is considerable
>> refinement in the model, so only a very small portion of the hex elements
>> are in immediate contact with quads.   Also you could think of places like
>> the tread in the tire where there is no reinforcement whatsoever.
>>
>> Another approach which I have considered is a wave propagation technique,
>> where in the first wave every hex immediately adjacent to a quad gets
>> direction cosines assigned (as you suggest).   Then you loop thru the
>> remaining elements and assign cosines from any adjacent quad or hex that
>> has cosines.   Eventually the direction cosines will propagate throughout
>> the model.   A major complication is that wavefronts will collide and then
>> you will have to choose which of several conflicting neighbor cosines to
>> adopt.  Averaging is one approach but certain structures give adjoining
>> cosines which are 180 degrees reversed, so averaging would give you an
>> indeterminate direction.
>>
>> I am toying now with some pseudo-variables, such as combinations of
>> radius and lateral location, combined with zoning, to try to find a
>> quantity that is unique for a local section of the geometry, to reduce the
>>  search size for each hex element.
>>
>> I am still hoping for a very clever scheme which someone may suggest
>> before I proceed with these much more brute force methods.
>>
>> Dennis
>>
>>
>>
>> *Sam Key Wrote:*
>>
>> *Dennis, *
>>
>> *Assuming for the moment that each quad 4-tuple is a finite element that
>> contains one or more tire reinforcement items, and that each quad 4-tuple
>> is "sandwiched" in between two hex 8-node finite elements, then the quad's
>> 4-tuple is also a surface facet of two different 8-node hexahedrons. Both
>> hexhedrons are the 'closest' hexhedrons to the quad. Given the usual
>> organization of 'element blocks' in the Exodus-II datum structures, the two
>> closest hexahedrons will be located on the surface of their respective
>> element blocks. *
>>
>> *Using material ID's which are also element block ID's, have the software
>> generate surface side-sets for each of these two element blocks specified
>> with these two material ID's. With luck, each member in the side-set will
>> be specified as a 2-tuple, (Elem# in the block, Quad-Face# in the hexah) *
>>
>> *With his info, you can confine your search to finding the side-set item
>> that has a 4-tuple that matches your quad's 4-tuple. The search is reduced
>> to a relatively small collection of hexahedral surface 4-tuple faces.  *
>>
>> *Hope this helps. *
>>
>> *Samuel W Key FMA Development, LLC 1005 39th Ave NE Great Falls, Montana
>> 59404 USA *
>>
>>
>>
>>
>>
>> *From:* Dennis Conklin
>> *Sent:* Thursday, August 20, 2015 3:52 PM
>> *To:* Paraview (paraview at paraview.org)
>> *Subject:* How to find the nearest quad element?
>>
>>
>>
>> All,
>>
>>
>>
>> I have an Exodus, multi-block model.  Most of the blocks are hex
>> elements, and some are layers of quads (tires are composite structures).  I
>> would like to establish local strains which are oriented in the direction
>> of the nearest quad layer.  To do this I need to identify, for each hex in
>> the model, which quad element in the model is closest to the hex.    Then I
>> can extract directions from the quad element and rotate the strain tensor
>> in the hex to these local coordinates.
>>
>>
>>
>> My question is,  is there some clever and efficient way to quickly
>> determine the nearest quad for each hex in the model.  Keep in mind that
>> there are multiple blocks of quads, but if there is some way to address the
>> quad blocks one at a time, I could make this work.
>>
>>
>>
>> The brute force way is:
>>
>> Loop over every hex in the model:
>>
>>       Loop over every quad in the model:
>>
>>              Calculate the distance between hex and quad
>>
>>              Smallest distance wins!
>>
>>
>>
>> That is a pretty brutally inefficient calc (several million hex elements)
>> that I am trying to avoid – any ideas about how best to approach this.
>> I’m hoping for some elegant way to use connectivity or something of that
>> sort.
>>
>>
>>
>> Thanks for looking
>>
>>
>>
>> Dennis
>>
>>
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