[vtkusers] Cannot make unstructured points isosurface

[Chris Scharver]

Hello,

I seem to be running into the often-encountered "my unstructured points aren't resulting in a contour" problem. I think I'm just tired and missing something obvious. I wonder if I'm just not setting up my initial data source propertly. The data is simply X-Y-Z with a scalar value. It has a regular topology, but I have none of the metadata about the topology easily available. There's no ordering available, so I read everything as a vtkUnstructuredGrid and set the scalar values. Each point is read and entered into the grid as a vtkVertex. The scalar values are read into a separate vtkFloatArray.

Here's the data parsing code:

  ifstream infile(this->FileName);
  if (infile) {
    vtkPoints* points = vtkPoints::New();
    vtkIdList* ids = vtkIdList::New();
    vtkFloatArray* velocities = vtkFloatArray::New();
    velocities->SetName("velocities");
    velocities->SetNumberOfComponents(1);
    vtkUnstructuredGrid* output = this->GetOutput();
    output->Allocate();
    float xyz[3];
    float vel;
    while (!infile.eof()) {
      if (infile >> xyz[1] >> xyz[0] >> xyz[2] >> vel) {
        // Perhaps really inefficient, but it seems to read ok...
        // Should I maybe use a different type of cell?
        vtkVertex* vertex = vtkVertex::New();
        vertex->GetPointIds()->InsertNextId(points->InsertNextPoint(xyz));
        output->InsertNextCell(vertex->GetCellType(), vertex->GetPointIds());
        velocities->InsertNextValue(vel);
      }
    }
    infile.close();
    output->SetPoints(points);
    output->GetPointData()->SetScalars(velocities);

I called output->GetScalarRange() to make sure that all the scalars were read properly and assigned, but I cannot seem to get a surface after applying the contour. I couldn't get color mapping to work properly. Here's the pipeline once the data has been read:

  vtkScrippsReader* dataReader = vtkScrippsReader::New();
  dataReader->SetFileName(argv[1]);
  // Scale the points to remove some distortion.
  vtkTransform* scaleTransform = vtkTransform::New();
  scaleTransform->Scale(1.0f, 1.0f, 0.0001f);
  vtkTransformFilter* scaler = vtkTransformFilter::New();
  scaler->SetInput(dataReader->GetOutput());
  scaler->SetTransform(scaleTransform);
  vtkContourFilter* contour = vtkContourFilter::New();
  contour->SetInput(scaler->GetOutput());
  contour->SetValue(0,  0.002f);
  vtkPolyDataMapper* mapper = vtkPolyDataMapper::New();
  mapper->SetInput(contour->GetOutput());

The contour is always empty, regardless of the value provided. I can see the points with a vtkDataSetMapper, although I cannot get the scalar values to result in coloring of the points.

  vtkLookupTable* lut = vtkLookupTable::New();
  lut->SetNumberOfColors(64);
  lut->SetTableRange(dataReader->GetOutput()->GetScalarRange());
  lut->Build();
  vtkDataSetMapper* dataMapper = vtkDataSetMapper::New();
  dataMapper->SetInput(scaler->GetOutput());
  dataMapper->SetLookupTable(lut);
  dataMapper->SetColorModeToMapScalars();
  dataMapper->SetScalarModeToUsePointData();
  dataMapper->ScalarVisibilityOn();

So I am just overlooking something? This all seems straightforward, but I've been lucky enough to use nicely formatted data files before, so now I am either not setting up my grid properly or I'm forgetting something in the pipeline. Any help would be tremendously appreciated.

Thanks,
Chris
--
Chris Scharver
Electronic Visualization Laboratory
The University of Illinois at Chicago
Ph: 312-996-3002   FAX: 312-413-7585
<http://www.evl.uic.edu/scharver/>