[vtkusers] interpolation

[tony hakki]

hi all;
I have some specific coordinates(x,y,z).  and 3D image which extension is raw.  I would like to get these coordinates scalars (grey level value) by interpolating.  I found out an example which seems what I would like to do. but in the following code I couldn't understand first  part of it where I show with red.   How ca i set the variable of output,input ? I could not understand the method of using this->........ Could someone help me on that confusing situation? I really need it much!
Thanks


here is example code:
void vtkCellDataToPointData::Execute()
{
  vtkIdType cellId, ptId;
  vtkIdType numCells, numPts;
  vtkDataSet *input= this->GetInput();
  vtkDataSet *output= this->GetOutput();
  vtkCellData *inPD=input->GetCellData();
  vtkPointData *outPD=output->GetPointData();
  vtkIdList *cellIds;
  float weight, *weights=new float[VTK_MAX_CELLS_PER_POINT];

  vtkDebugMacro(<<"Mapping cell data to point data");

  // First, copy the input to the output as a starting point
  output->CopyStructure( input );

  cellIds = vtkIdList::New();
  cellIds->Allocate(VTK_MAX_CELLS_PER_POINT);

  if ( (numPts=input->GetNumberOfPoints()) < 1 )
    {
    vtkErrorMacro(<<"No input point data!");
    cellIds->Delete();
    return;
    }
  
  // Pass the point data first. The fields and attributes
  // which also exist in the cell data of the input will
  // be over-written during CopyAllocate
  output->GetPointData()->PassData(input->GetPointData());

  // notice that inPD and outPD are vtkCellData and vtkPointData; respectively.
  // It's weird, but it works.
  outPD->CopyAllocate(inPD,numPts);

  int abort=0;
  vtkIdType progressInterval=numPts/20 + 1;
  for (ptId=0; ptId < numPts && !abort; ptId++)
    {
    if ( !(ptId % progressInterval) )
      {
      this->UpdateProgress((float)ptId/numPts);
      abort = GetAbortExecute();
      }

    input->GetPointCells(ptId, cellIds);
    numCells = cellIds->GetNumberOfIds();
    if ( numCells > 0 )
      {
      weight = 1.0 / numCells;
      for (cellId=0; cellId < numCells; cellId++)
	{
	weights[cellId] = weight;
	}
      outPD->InterpolatePoint(inPD, ptId, cellIds, weights);
      }
    else
      {
      outPD->NullPoint(ptId);
      }
    }

  if ( this->PassCellData )
    {
    output->GetCellData()->PassData(input->GetCellData());
    }

  cellIds->Delete();
  delete [] weights;
}


 
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