[vtkusers] How to visualize segments/surfaces selectively: vtkLookupTable with vtkContourFilter

[Divya Rathore]

I have a 16bit cube data that has various segments of unique grey levels. I
want to visualize each of these segments selectively using a slider (just
the surface visualization is good enough) . This slider ranges from the min
to the max of the grey levels in that cube.

I expected isosurfaces to do that job well. But it seems any level of
isovalue behaves somewhat like thresholding and essentially divides the
grey levels in 2 parts - the ones lower than the isovalue and the ones
higher than the isovalue. This means that all of the segments higher than
the selected would get 'iso-surfaced' (if I may say so!) as well (as in
attached image).

How can I view just one of the segments at a time, interactively?
Ideally in the image, I should be seeing just 1 of those structures at a
time (it currently shows 3).

here's part of the code:


// short data

vtkSmartPointer<vtkImageReader> v16 =
vtkSmartPointer<vtkImageReader>::New();
v16->SetFileName(argv[2]);
v16->SetFileDimensionality(3);
v16->SetDataScalarTypeToUnsignedShort();
v16->SetDataByteOrderToLittleEndian();
v16->SetNumberOfScalarComponents(1);
v16->SetDataExtent(0,width-1, 0,height-1, 0,depth-1);
v16->SetDataSpacing (1.0, 1.0, 1.0);
v16->Update();

double range[2];
v16->GetOutput()->GetPointData()->GetScalars()->GetRange(range);
std::cout << "Range: " << range[0] << " , " << range[1] << std::endl;
double midpoint = (range[1]-range[0])/2;

//Now build a LUT
vtkSmartPointer<vtkLookupTable> lookupTable =
vtkSmartPointer<vtkLookupTable>::New();
lookupTable->SetNumberOfTableValues(range[1]);
lookupTable->SetTableRange(range[0], range[1]);
// Firstly, set all transparent
for(int i=range[0]; i<range[1]; ++i)
{
lookupTable->SetTableValue( i, .66, .92, .33, 0.0 ); //some shade of green
but transparent
}
// Make that 1 value corresponding to slider visible
lookupTable->SetTableValue( (int) midpoint, .66, .92, .33, 1.0 ); //same
color as above, but visible
lookupTable->Build();
//Usual steps as in Medical3 example
vtkSmartPointer<vtkContourFilter> Extractor =
vtkSmartPointer<vtkContourFilter>::New();
Extractor->SetInputConnection( v16->GetOutputPort());
Extractor->SetNumberOfContours(1);
// set an isovalue. in this case, the midpoint of the greyscales
Extractor->GenerateValues(1, midpoint, midpoint);
Extractor->Update();

vtkSmartPointer<vtkPolyDataNormals> Normals =
vtkSmartPointer<vtkPolyDataNormals>::New();
Normals->SetInputConnection(grainExtractor->GetOutputPort());
Normals->ReleaseDataFlagOn();
Normals->SetFeatureAngle(60.0);
Normals->Update();

vtkSmartPointer<vtkStripper> Stripper =
vtkSmartPointer<vtkStripper>::New();
Stripper->SetInputConnection(grainNormals->GetOutputPort());
Stripper->ReleaseDataFlagOn();
Stripper->Update();

// An addition to Medical 3 example: Provide LUT to Mapper
vtkSmartPointer<vtkPolyDataMapper> Mapper =
vtkSmartPointer<vtkPolyDataMapper>::New();
Mapper->SetInputConnection(grainStripper->GetOutputPort());
Mapper->ReleaseDataFlagOn();
Mapper->ScalarVisibilityOn();
Mapper->SetScalarRange(lookupTable->GetRange());
Mapper->SetLookupTable(lookupTable);
Mapper->Update();
vtkSmartPointer<vtkActor> Actor =
vtkSmartPointer<vtkActor>::New();
Actor->SetMapper(grainMapper);
Actor->GetProperty()->SetDiffuseColor(.66, .92, .33);
Actor->GetProperty()->SetSpecular(.3);
Actor->GetProperty()->SetSpecularPower(20);
Actor->GetProperty()->SetOpacity(1.0);


// Rest of the code handles a slider that tries to change the isovalue
// But doesn't reflect the change :(

What's wrong in my approach of using vtkLookupTable with vtkContourFilter?
Is there an alternate?


best regards,
Divya Rathore
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