Computing Isosurface on a chosen attribute

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1

Hi,

I work with an unstructured grid containing multiple attributes. I wish to process the isosurface of one of these attributes, which has been prototyped with Paraview successfully. I thrive to do the same with VTK based on the vtkFlyingEdge3D example.

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The main point is that I want to express the contour levels in terms of this attribute value range. However, when using vtkVoxelModeler and vtkImageData as preprocessing for vtkFlyingEdges3D, I can only express contour in terms of values in range [0;1] (i.e. [background; foreground] values of vtkVoxelModeller).

How should I adapt my pipeline to process contours of this attribute?

Here is a summary of my program inspired by vtkFlyingEdges3D

String propertyName = "temp";
double[] levels = {800, 1000, 1200, 1400, 1600, 1800, 2000};
vtkUnstructuredGrid ugrid = ... // load exodus file
ugrid.GetPointData().SetActiveScalars(propertyName);

// Convert to poly data
vtkGeometryFilter toPoly = new vtkGeometryFilter();
toPoly.SetInputData(uGrid);

// Converts to a voxel representation
vtkVoxelModeller voxelModeller = new vtkVoxelModeller();
voxelModeller.SetSampleDimensions(10, 10, 10);
voxelModeller.SetScalarTypeToDouble();
voxelModeller.SetModelBounds(toPoly.GetOutput().GetBounds());
voxelModeller.SetInputConnection(toPoly.GetOutputPort());

// Copy voxel to image data structure
vtkImageData volume = new vtkImageData();
volume.DeepCopy(voxelModeller.GetOutput());

// Apply contour surface to voxels
vtkFlyingEdges3D isoSurface = new vtkFlyingEdges3D();
isoSurface.SetInputData(volume);
isoSurface.SetNumberOfContours(levels.length);
for (int i = 0; i < levels.length; i++) {
  isoSurface.SetValue(i, levels[i]); 
}
isoSurface.Update();

System.out.println("Number of contour : " + isoSurface.GetNumberOfContours());
System.out.println("Number of cells : " + isoSurface.GetOutput().GetNumberOfCells());

I got an empty output

Number of contour : 7
Number of cells : 0 // <<<<<<<< PROBLEM

If I however uses levels in [0;1]

double[] levels = {0.08, 0.10, 0.12, 0.14, 0.16, 0.18, 0.20};

I got something

Number of contour : 7
Number of cells : 5488
2

Hi Martin,

It seems your data is already in a 3D cells format. This means you could use something like the vtkContourFilter directly on the grid (https://vtk.org/doc/nightly/html/classvtkContourFilter.html#details) or vtkMarchingContourFilter.

So, you would have something like:

String propertyName = "temp";
double[] levels = {800, 1000, 1200, 1400, 1600, 1800, 2000};
vtkUnstructuredGrid ugrid = ... // load exodus file
ugrid.GetPointData().SetActiveScalars(propertyName);

vtkNew<vtkContourFilter> isoSurface;
isoSurface->SetInputData(ugrid);
for (int i = 0; i < levels.length; i++) {
  isoSurface.SetValue(i, levels[i]); 
}
isoSurface.Update();

Cheers,
Hilco