[vtkusers] Thresholding Bug?

[Chris Scharver]

Hello,

I'm having a strange experience trying to threshold some data. I cannot seem to get a threshold above 0.0. I always get an empty data set. I read the data into a structured grid. The scalar range is (-0.0767 0.0824), and I can confirm that reading the output from the vtkAssignAttribute operation (aa->GetOutput()->GetScalarRange()). Any points with scalars above 0.0 are ignored by the thresholding. Am I not assigning something properly? I'm using the current cvs version.


  // Filter that data from the data object to a data set.
  vtkDataObjectToDataSetFilter* dods = vtkDataObjectToDataSetFilter::New();
  dods->SetInput(dataReader->GetOutput());
  dods->SetDataSetTypeToStructuredGrid();
  //dods->SetDataSetTypeToRectilinearGrid();
  dods->DefaultNormalizeOn();
  dods->SetPointComponent(0, "latitude", 0);
  dods->SetPointComponent(1, "longitude", 0);
  dods->SetPointComponent(2, "depth", 0);
  dods->SetDimensions(dataReader->GetDimensions());

  // Move the velocity field to the data.
  vtkRearrangeFields* rf = vtkRearrangeFields::New();
  rf->SetInput(dods->GetOutput());
  rf->AddOperation(vtkRearrangeFields::MOVE, "velocity",
                   vtkRearrangeFields::DATA_OBJECT,
                   vtkRearrangeFields::POINT_DATA);

  // Assign the velocity field as the scalar value.
  vtkAssignAttribute* aa = vtkAssignAttribute::New();
  aa->SetInput(rf->GetOutput());
  aa->Assign("velocity", vtkDataSetAttributes::SCALARS,
             vtkAssignAttribute::POINT_DATA);
  aa->Update();

  // Create the lower threshold.
  float* rng = aa->GetOutput()->GetScalarRange();
  cerr << "aa scalar range: " << rng[0] << " " << rng[1] << endl;
  vtkThresholdPoints* lowThresh = vtkThresholdPoints::New();
  // this works: lowThresh->ThresholdByUpper(0.0f);
  lowThresh->ThresholdByLower(0.0f); // this does not!
  lowThresh->SetInput(aa->GetOutput());
  // This splatter complains that there is no data!
  vtkGaussianSplatter* lowSplat = vtkGaussianSplatter::New();
  lowSplat->SetInput(lowThresh->GetOutput());
  lowSplat->SetSampleDimensions(dimsize, dimsize, dimsize);
  lowSplat->SetRadius(0.02f);
  lowSplat->ScalarWarpingOff();

The threshold seems to calculate the results incorrectly. I can confirm that the data has scalars both above and less than 0. If I skip the threshold altogether (ie. sending the data directly to the splatter) than all points are represented.

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/>