1.連通區域分析
許多圖形數據中，並非只包含一個對象（連通區域）。而在處理這些圖形數據時，有時需要對每一個對象單獨處理或者讓其單獨顯示。比如，利用MarchingCube方法提取三維圖像中的等值面，得到的結果往往是存在多個連通的對象區域，這是就需要對圖形數據做連通區域分析，提取每個連通區域並計算其屬性信息，以此來得到需要的連通區域。
下面一個例子來分析VTK中如何對圖形數據做連通區域分析：
1 #include <vtkAutoInit.h> 2 VTK_MODULE_INIT(vtkRenderingOpenGL); 3 VTK_MODULE_INIT(vtkRenderingFreeType); 4 VTK_MODULE_INIT(vtkInteractionStyle); 5 6 #include <vtkSmartPointer.h> 7 #include <vtkSphereSource.h> 8 #include <vtkConeSource.h> 9 #include <vtkAppendPolyData.h> 10 #include <vtkPolyDataConnectivityFilter.h> 11 #include <vtkPolyDataMapper.h> 12 #include <vtkActor.h> 13 #include <vtkProperty.h> 14 #include <vtkRenderer.h> 15 #include <vtkRenderWindow.h> 16 #include <vtkRenderWindowInteractor.h> 17 int main() 18 { 19 vtkSmartPointer<vtkSphereSource> sphereSource = 20 vtkSmartPointer<vtkSphereSource>::New(); 21 sphereSource->SetRadius(10); 22 sphereSource->SetThetaResolution(10); 23 sphereSource->SetPhiResolution(10); 24 sphereSource->Update(); 25 26 vtkSmartPointer<vtkConeSource> coneSource = 27 vtkSmartPointer<vtkConeSource>::New(); 28 coneSource->SetRadius(5); 29 coneSource->SetHeight(10); 30 coneSource->SetCenter(25, 0, 0); 31 coneSource->Update(); 32 33 vtkSmartPointer<vtkAppendPolyData> appendFilter = 34 vtkSmartPointer<vtkAppendPolyData>::New(); 35 appendFilter->AddInputData(sphereSource->GetOutput()); 36 appendFilter->AddInputData(coneSource->GetOutput()); 37 appendFilter->Update(); 38 39 vtkSmartPointer<vtkPolyDataConnectivityFilter> connectivityFilter = 40 vtkSmartPointer<vtkPolyDataConnectivityFilter>::New(); 41 connectivityFilter->SetInputData(appendFilter->GetOutput()); 42 connectivityFilter->SetExtractionModeToCellSeededRegions(); 43 connectivityFilter->AddSeed(100); 44 connectivityFilter->Update(); 45 46 vtkSmartPointer<vtkPolyDataMapper> originalMapper = 47 vtkSmartPointer<vtkPolyDataMapper>::New(); 48 originalMapper->SetInputConnection(appendFilter->GetOutputPort()); 49 originalMapper->Update(); 50 vtkSmartPointer<vtkActor> originalActor = 51 vtkSmartPointer<vtkActor>::New(); 52 originalActor->SetMapper(originalMapper); 53 54 vtkSmartPointer<vtkPolyDataMapper> extractedMapper = 55 vtkSmartPointer<vtkPolyDataMapper>::New(); 56 extractedMapper->SetInputConnection(connectivityFilter->GetOutputPort()); 57 extractedMapper->Update(); 58 vtkSmartPointer<vtkActor> extractedActor = 59 vtkSmartPointer<vtkActor>::New(); 60 extractedActor->SetMapper(extractedMapper); 61 / 62 double leftViewport[4] = { 0.0, 0.0, 0.5, 1.0 }; 63 double rightViewport[4] = { 0.5, 0.0, 1.0, 1.0 }; 64 65 vtkSmartPointer<vtkRenderer> leftRenderer = 66 vtkSmartPointer<vtkRenderer>::New(); 67 leftRenderer->SetViewport(leftViewport); 68 leftRenderer->AddActor(originalActor); 69 leftRenderer->SetBackground(1, 0, 0); 70 71 vtkSmartPointer<vtkRenderer> rightRenderer = 72 vtkSmartPointer<vtkRenderer>::New(); 73 rightRenderer->SetViewport(rightViewport); 74 rightRenderer->AddActor(extractedActor); 75 rightRenderer->SetBackground(0, 0, 0); 76 77 vtkSmartPointer<vtkRenderWindow> renderWindow = 78 vtkSmartPointer<vtkRenderWindow>::New(); 79 renderWindow->AddRenderer(leftRenderer); 80 renderWindow->AddRenderer(rightRenderer); 81 renderWindow->SetSize(640, 320); 82 renderWindow->Render(); 83 renderWindow->SetWindowName("PolyDataConnectedCompExtract"); 84 85 leftRenderer->ResetCamera(); 86 rightRenderer->SetActiveCamera(leftRenderer->GetActiveCamera()); 87 88 vtkSmartPointer<vtkRenderWindowInteractor> interactor = 89 vtkSmartPointer<vtkRenderWindowInteractor>::New(); 90 interactor->SetRenderWindow(renderWindow); 91 interactor->Initialize(); 92 interactor->Start(); 93 return 0; 94 }輸出結果為：
這個例子夠早了一個含有多個連通區域的模型數據。vtkAppendPolyData可以實現vtkPolyData的合並，使用該類可以方便地構造含有多個連通區域的數據，該類型接收兩個或者多個vtkPolyData數據輸入，合並結果包含輸入數據的所有幾何和拓撲數據。若輸入為兩個或者多個數據都含有點屬性數據，則將其存儲值輸出結果中；對於單元屬性數據亦是如此。
2.VTKPolyDataConnectivityFilter類解析
vtk中的vtkPolyDataConnectivityFilter類可以用於實現連通區域分析，該類接受vtkPolyData數據作為輸入。集體使用如下：
1 vtkSmartPointer<vtkPolyDataConnectivityFilter> connectivityFilter = 2 vtkSmartPointer<vtkPolyDataConnectivityFilter>::New(); 3 connectivityFilter->SetInputData(appendFilter->GetOutput()); 4 connectivityFilter->SetExtractionModeToCellSeededRegions(); 5 connectivityFilter->AddSeed(100); 6 connectivityFilter->Update();etExtractionModeToLargestRegion()：用於提取具有最多點數的連通區域；SetExtractionModeToAllRegions()：該模式主要用於連通區域標記，配合函數ColorRegionsOn()使用，在連通區域像是的同時，生成一個名為RegionId的點屬性數據。
SetExtractionModeToSpecifiedRegions()：該模式用於提取一個或多個連通區域，在該模式下，需要通過AddSpecifiedRegion()來添加西葯提取的區域號，區域號從零開始。SetExtractionModeToClosestPointRegion()：該模式需要使用SetClosestPoint()函數設置一個空間點坐標，執行結果為離該點最近的連通區域。SetExtractionModeToPointSeededRegions()：該模式下需要使用AddSeed()函數添加種子點，提取種子點所在的區域。SetExtractionModeToCellSeededRegions()：該模式下需要使用AddSeed()函數調價種子單元，提取種子單元所在的區域。