[vtkusers] vtkQuadricDecimation and colors

[Olli]

Hi,

I'm rendering elevation data. Originally data is a structured grid and very
dense. But looks fine. When I try to reduce number of polygons using
vtkQuadricDecimation I loose all colors and get a gray scale image. I wonder
why? What does decimation do to the data so that mapper cannot color it any
more?

Btw. Using vtkDecimatePro solves the coloring problem. But the question
remains: why colors disappear when I use vtkQuadricDecimation? Why?

The pipeline I use is below. (No smart pointers, I know. It's a sample and
easier to read, when not using smart pointers). It works just fine if I skip
quadric decimation.

Thanks,

Olli


    vtkImageImport* reader = vtkImageImport::New();
        // import settings
        // ...
    reader->Update();

    vtkDataSetSurfaceFilter* filter = vtkDataSetSurfaceFilter::New();
    filter->SetInputConnection(reader->GetOutputPort());
    reader->Delete();
    filter->ReleaseDataFlagOn();
    filter->Update();

    vtkWarpScalar* warp = vtkWarpScalar::New();
    warp->SetInputConnection(filter->GetOutputPort());
    filter->Delete();
    warp->SetScaleFactor(3);
    warp->Update();

    vtkQuadricClustering* cluster = vtkQuadricClustering::New();
    cluster->SetInputConnection(warp->GetOutputPort());
    warp->Delete();
    cluster->AutoAdjustNumberOfDivisionsOff();
    cluster->SetNumberOfDivisions(240, 240, 10);
    cluster->PreventDuplicateCellsOn();
    cluster->UseInputPointsOn();
    cluster->Update();

    vtkQuadricDecimation *dec=vtkQuadricDecimation ::New();
    dec->SetInputConnection(cluster->GetOutputPort());
    cluster->Delete();
    dec->SetTargetReduction(.80);
    dec->Update();

    // color map for terrain
    vtkColorTransferFunction* lut = vtkColorTransferFunction::New();
    lut->AddHSVSegment(1, 0.3, 0.7, 0.7, 2000, 0.1, 0.7, 0.7); // terrain
    lut->AddHSVPoint(0, 0.667, 0.7, 1); // sea level

    vtkPolyDataMapper* mapper = vtkPolyDataMapper::New();
    mapper->SetInputConnection(dec->GetOutputPort());
    dec->Delete();
    mapper->ScalarVisibilityOn();
    mapper->SetScalarRange(0, 1000);
    mapper->SetLookupTable(lut);
    lut->Delete();
    mapper->Update();
   ...
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