[Paraview] [EXT] Re: Good neighbor filter

Fri Feb 16 01:18:59 EST 2018

Hi,

I have experienced a similar situation with a vtkUnstructuredGrid, and
written a programmable filter something like:
----
import numpy as np

input = self.GetInput()
output = self.GetOutput()

numCells = input.GetNumberOfCells()

volChange = vtk.vtkFloatArray()
volChange.SetName("volumeChange")
volChange.SetNumberOfComponents(1)
volChange.SetNumberOfTuples(numCells)

for cellId in range(numCells):
  cell = input.GetCell(cellId)

  maxVol = -vtk.VTK_DOUBLE_MAX
  minVol = vtk.VTK_DOUBLE_MAX

  nFaces = cell.GetNumberOfFaces()
  for faceId in range(nFaces):
    pntIds = cell.GetFace(faceId).GetPointIds()

    neighbors = vtk.vtkIdList()
    input.GetCellNeighbors(cellId, pntIds, neighbors)

    numNei = neighbors.GetNumberOfIds()
    for num in range(numNei):
      neiId = neighbors.GetId(num)
      nei = input.GetCell(neiId)
      if nei.GetCellType() == vtk.VTK_TETRA:
        p1 = input.GetPoint(nei.GetPointId(0))
        p2 = input.GetPoint(nei.GetPointId(1))
        p3 = input.GetPoint(nei.GetPointId(2))
        p4 = input.GetPoint(nei.GetPointId(3))
        vol = vtk.vtkTetra.ComputeVolume(p1, p2, p3, p4)
        maxVol = np.maximum(maxVol, vol)
        minVol = np.minimum(minVol, vol)

  input.GetCell(cellId)
  #print(str(cellId) + ':' + str(maxVol/minVol))
  volChange.SetValue(cellId, maxVol/minVol)

output.GetCellData().AddArray(volChange)
----

Notice this computes the volumes of all cells that neighbor a cell on its
faces.

Thanks,

2018-02-15 23:17 GMT+09:00 Dennis Conklin <dennis_conklin at goodyear.com>:

> Andy,
>
>
>
> Thanks for that hint – I think I get the idea.   This is a “as time is
> available” project, so I’ll start exploring it, but I appreciate being
> pointed in the right direction.
>
>
>
> Dennis
>
>
>
> *From:* Andy Bauer [mailto:andy.bauer at kitware.com]
> *Sent:* Wednesday, February 14, 2018 1:51 PM
> *To:* Dennis Conklin <dennis_conklin at goodyear.com>
> *Cc:* Paraview (paraview at paraview.org) <paraview at paraview.org>
> *Subject:* [EXT] Re: [Paraview] Good neighbor filter
>
>
>
>  *WARNING - External email; exercise caution.*
>
>
>
> Hi Dennis,
>
> I'm assuming you're dealing with a vtkUnstructuredGrid (for the
> topologically regular grids you should just use the extent information).
> You'll want to look at the GetCellNeighbors() method --
> https://www.vtk.org/doc/nightly/html/classvtkUnstructuredGrid.html#
> ac532485599a5d92acf4d9ca1e8818bfc
> <https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.vtk.org%2Fdoc%2Fnightly%2Fhtml%2FclassvtkUnstructuredGrid.html%23ac532485599a5d92acf4d9ca1e8818bfc&data=01%7C01%7Cdennis_conklin%40goodyear.com%7Cf1004f8cac4a459ffdb908d573dbed3d%7C939e896692854a9a9f040887efe8aae0%7C0&sdata=L4bbRrKp82mtwWrnYEN6BqxNWNOkPVGp9Oa%2BMj7I7KU%3D&reserved=0>.
> Here, cellId is the cell you want to get the neighbors from, ptIds is the
> list of points that need to be shared by both cells and cellIds is the
> return list. You'll have to iterate over all points of the cell you're
> interested in (i.e. call GetCellNeighbors() 8 times for a hex).
>
> The basic algorithm is:
>
> loop over cells:
>
>   for each cell, loop over all of its points
>
>     for each point call GeCellNeighbors(cellid, point id list with a
> single point)
>
>       loop through cellids to compare cell sizes
>
>
>
> Please let me know if this isn't clear enough to get you going...
>
> Cheers,
>
> Andy
>
>
>
> On Wed, Feb 14, 2018 at 1:38 PM, Dennis Conklin <
> dennis_conklin at goodyear.com> wrote:
>
> All,
>
>
>
> I am looking to calculate a mesh quality measure that would be the ratio
> of the max/min of the element volumes of each element and all it’s
> neighbors (other elements with common nodes).  I intend to use this to
> quantify grid refinement transitions and perhaps establish some design
> standards for them.    I have tried Gradient of Element Volume, but I need
> to eliminate the distance part of that to get the number that I want.
> So, if I have a hex element in a regular grid,  I would expect to have 26
> “neighbor” elements plus the original element.    The number I want is
> (max of 27 element volumes)/(min of 27 element volumes).    This quantity
> will highlight mesh refinement transitions.
>
>
>
> My question (at last) is:    how do I find all the neighbor elements
> (share at least 1 node) of each element in my model?   I’d like to do this
> in a Programmable Filter.  I’m afraid I don’t know much about how
> connectivity is implemented in vtk.
>
>
>
> Dennis
>
>
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