[Paraview] [EXT] Re: Good neighbor filter

Fri Feb 16 08:07:04 EST 2018

Kenichiro,

Thanks for the idea.   This looks very good and I very much appreciate you sharing that with me.

Dennis

From: kenichiro yoshimi [mailto:rccm.kyoshimi at gmail.com]
Sent: Friday, February 16, 2018 1:19 AM
To: Dennis Conklin <dennis_conklin at goodyear.com>
Cc: Andy Bauer <andy.bauer at kitware.com>; Paraview (paraview at paraview.org) <paraview at paraview.org>
Subject: Re: [Paraview] [EXT] Re: Good neighbor filter

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<mailto: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<mailto:andy.bauer at kitware.com>]
Sent: Wednesday, February 14, 2018 1:51 PM
To: Dennis Conklin <dennis_conklin at goodyear.com<mailto:dennis_conklin at goodyear.com>>
Cc: Paraview (paraview at paraview.org<mailto:paraview at paraview.org>) <paraview at paraview.org<mailto: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<mailto: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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