[vtk-developers] New nonlinear celltypes

[Soeren Gebbert]

David C. Thompson wrote:

>On Mon, 2006-01-09 at 13:33, John Platt wrote:
>  
>
>>... I have just had a quick look at the version of
>>vtkQuadraticHexahedron::Contour() I am using from 4.4. The call to the
>>linear Hex contouring
>>
>>    this->Hex->Contour(value,this->Scalars,locator,verts,lines,polys,
>>                       this->PointData,outPd,this->CellData,0,outCd);
>>
>>takes the local PointData and CellData from Subdivide(). Your call
>>
>>    this->Hex->Contour(value,this->Scalars,locator,verts,lines,polys,
>>                       inPd, outPd, inCd, cellId, outCd);
>>
>>passes the dataset point and cell data.
>>    
>>
>You know, I looked at that and assumed that all Subdivide() did was make
>a local copy with 27 instead of 20 nodes. Since the 27-node hex didn't
>need to generate mid-face and body points, I thought it would be OK to
>pass them directly and didn't even think about indexing, but you're
>right... that might cause trouble.
>
>  
>
I thought it would be smart to pass the inPd and inCd direct to the 
clipping/contouring methods to spare some
memory. (this->PointData, this->CellData and this->CellScalars are not 
needed anymore, will be not declared or initialized).
Because, as David sayd, the 27 node Hex dont need subdivision or data 
interpolation.

But i made two implementation's:
1.) with data interpolation (like vtkQuadrataicHexahedron)

//----------------------------------------------------------------------------
// Clip this triquadratic hex using scalar value provided. Like contouring,
// except that it cuts the hex to produce tetrahedra.
void
vtkTriQuadraticHexahedron::Clip (double value,
                 vtkDataArray * cellScalars,
                 vtkPointLocator * locator,
                 vtkCellArray * tets,
                 vtkPointData * inPd,
                 vtkPointData * outPd,
                 vtkCellData * inCd, vtkIdType cellId, vtkCellData * 
outCd, int insideOut)
{
  int i, j;

  vtkPointData *PointData = vtkPointData::New();
  vtkCellData *CellData = vtkCellData::New();
  vtkDoubleArray *CellScalars = vtkDoubleArray::New();
 
  PointData->Initialize();
  CellData->Initialize();
  CellScalars->Initialize();
  PointData->CopyAllocate(inPd,27);
  CellData->CopyAllocate(inCd,8);
  CellScalars->SetNumberOfTuples(27);

  for (i=0; i<27; i++)
    {
    PointData->CopyData(inPd,this->PointIds->GetId(i),i);
    CellScalars->SetValue( i, cellScalars->GetTuple1(i));
    }
  CellData->CopyData(inCd,cellId,0);
 

  //clip each linear hex separately
  for (i = 0; i < 8; i++)
    {
      for (j = 0; j < 8; j++)
    {
      this->Hex->Points->SetPoint (j, this->Points->GetPoint 
(LinearHexs[i][j]));
      this->Hex->PointIds->SetId (j, LinearHexs[i][j]);
      this->Scalars->SetValue (j, CellScalars->GetTuple1 
(LinearHexs[i][j]));
    }
      this->Hex->Clip (value, this->Scalars, locator, tets, PointData, 
outPd, CellData, cellId, outCd, insideOut);
    }

    PointData->Delete();
    CellData->Delete();
    CellScalars->Delete();
}


2.) without data interpolation

//----------------------------------------------------------------------------
// Clip this triquadratic hex using scalar value provided. Like contouring,
// except that it cuts the hex to produce tetrahedra.
void
vtkTriQuadraticHexahedron::Clip (double value,
                 vtkDataArray * cellScalars,
                 vtkPointLocator * locator,
                 vtkCellArray * tets,
                 vtkPointData * inPd,
                 vtkPointData * outPd,
                 vtkCellData * inCd, vtkIdType cellId, vtkCellData * 
outCd, int insideOut)
{
  int i, j;

  //clip each linear hex separately
  for (i = 0; i < 8; i++)
    {
      for (j = 0; j < 8; j++)
    {
      this->Hex->Points->SetPoint (j, this->Points->GetPoint 
(LinearHexs[i][j]));
      this->Hex->PointIds->SetId (j, LinearHexs[i][j]);
      this->Scalars->SetValue (j, cellScalars->GetTuple1 
(LinearHexs[i][j]));
    }
      this->Hex->Clip (value, this->Scalars, locator, tets, inPd, outPd, 
inCd, cellId, outCd, insideOut);
    }
}


Booth have the same problems, so the implementation

this->Hex->Clip (value, this->Scalars, locator, tets, inPd, outPd, inCd, cellId, outCd, insideOut);

seems to be correct (incorrect???) too. (numbering and stuff)


>>I don't know if this has changed at version 5.
>>    
>>
>Nope. Although as of 4.4.2, there was a bug in clipping and contouring
>preventing them from working on more than a single cell because the
>point ids were being set incorrectly. It looks like Soeren got that part
>right. To see the difference run 
>  cd VTK/Common
>  cvs diff -r 1.21 -r 1.22 vtkQuadraticHexahedron.cxx
>
>	David
>
>
>  
>