1.点云重建

虽然Delaunay三角剖分算法可以实现网格曲面重建，但是其应用主要在二维剖分，在三维空间网格生成中遇到了问题。因为在三维点云曲面重建中，Delaunay条件不在满足，不仅基于最大最小角判断的对角线交换准则不在成立，而且基于外接圆判据的Delaunay三角化也不能保证网格质量。 VTKSurfaceReconstructionFilter则实现了一种隐式曲面重建方法，即将曲面看做一个符号距离函数的等值面，曲面内外的距离值得符号相反，而零等值面即为所求的曲面。该方法需要对点云数据进行网格划分，然后估算每个点的切平面和方向，并以每个点与最近的切平面距离来近似表面距离。这样即可得到一个符号距离的体数据。这样，我们就可以利用VTKContourFilter来提取零等值面即可得到相应的网格。 利用人脸点云数据进行人脸网格曲面重建实例如下： #include <vtkAutoInit.h> VTK_MODULE_INIT(vtkRenderingOpenGL); VTK_MODULE_INIT(vtkRenderingFreeType); VTK_MODULE_INIT(vtkInteractionStyle); #include <vtkSmartPointer.h> #include <vtkPolyDataReader.h> #include <vtkPolyData.h> #include <vtkSurfaceReconstructionFilter.h> #include <vtkContourFilter.h> #include <vtkVertexGlyphFilter.h> #include <vtkPolyDataMapper.h> #include <vtkActor.h> #include <vtkRenderer.h> #include <vtkCamera.h> #include <vtkRenderWindow.h> #include <vtkRenderWindowInteractor.h> #include <vtkProperty.h> int main() { vtkSmartPointer<vtkPolyDataReader> reader = vtkSmartPointer<vtkPolyDataReader>::New(); reader->SetFileName("fran_cut.vtk"); reader->Update(); vtkSmartPointer<vtkPolyData> points = vtkSmartPointer<vtkPolyData>::New(); points->SetPoints(reader->GetOutput()->GetPoints()); //获得网格模型中的几何数据：点集 vtkSmartPointer<vtkSurfaceReconstructionFilter> surf = vtkSmartPointer<vtkSurfaceReconstructionFilter>::New(); surf->SetInputData(points); surf->SetNeighborhoodSize(20); surf->SetSampleSpacing(0.005); surf->Update(); vtkSmartPointer<vtkContourFilter> contour = vtkSmartPointer<vtkContourFilter>::New(); contour->SetInputConnection(surf->GetOutputPort()); contour->SetValue(0, 0.0); contour->Update(); // vtkSmartPointer <vtkVertexGlyphFilter> vertexGlyphFilter = vtkSmartPointer<vtkVertexGlyphFilter>::New(); vertexGlyphFilter->AddInputData(points); vertexGlyphFilter->Update(); vtkSmartPointer<vtkPolyDataMapper> pointMapper = vtkSmartPointer<vtkPolyDataMapper>::New(); pointMapper->SetInputData(vertexGlyphFilter->GetOutput()); pointMapper->ScalarVisibilityOff(); vtkSmartPointer<vtkActor> pointActor = vtkSmartPointer<vtkActor>::New(); pointActor->SetMapper(pointMapper); pointActor->GetProperty()->SetColor(1, 0, 0); pointActor->GetProperty()->SetPointSize(4); vtkSmartPointer<vtkPolyDataMapper> contourMapper = vtkSmartPointer<vtkPolyDataMapper>::New(); contourMapper->SetInputData(contour->GetOutput()); vtkSmartPointer<vtkActor> contourActor = vtkSmartPointer<vtkActor>::New(); contourActor->SetMapper(contourMapper); /// double pointView[4] = { 0, 0, 0.5, 1 }; double contourView[4] = { 0.5, 0, 1, 1 }; vtkSmartPointer<vtkRenderer> pointRender = vtkSmartPointer<vtkRenderer>::New(); pointRender->AddActor(pointActor); pointRender->SetViewport(pointView); pointRender->SetBackground(1, 1, 1); vtkSmartPointer<vtkRenderer> contourRender = vtkSmartPointer<vtkRenderer>::New(); contourRender->AddActor(contourActor); contourRender->SetViewport(contourView); contourRender->SetBackground(0, 1, 0); pointRender->GetActiveCamera()->SetPosition(0, -1, 0); pointRender->GetActiveCamera()->SetFocalPoint(0, 0, 0); pointRender->GetActiveCamera()->SetViewUp(0,0,1); pointRender->GetActiveCamera()->Azimuth(30); pointRender->GetActiveCamera()->Elevation(30); pointRender->ResetCamera(); contourRender->SetActiveCamera(pointRender->GetActiveCamera()); vtkSmartPointer<vtkRenderWindow> rw = vtkSmartPointer<vtkRenderWindow>::New(); rw->AddRenderer(pointRender); rw->AddRenderer(contourRender); rw->SetSize(640, 320); rw->SetWindowName("3D Surface Reconstruction "); rw->Render(); vtkSmartPointer<vtkRenderWindowInteractor> rwi = vtkSmartPointer<vtkRenderWindowInteractor>::New(); rwi->SetRenderWindow(rw); rwi->Initialize(); rwi->Start(); return 0; } 使用VTKSurfaceReconstructionFilter时，主要涉及两个参数，分别使用函数SetNeighborhoodSize()和SetSampleSpacing()进行设置。 SetNeighborhoodSize：设置邻域点的个数；而这些邻域点则用来估计每个点的局部切平面。邻域点的个数默认为20，能够处理大多数重建问题。个数设置越多，计算消耗时间越长。当点云分布严重不均匀情况下，可以考虑增加该值。 SetSampleSpacing：用于设置划分网格的网格间距，间距与小，网格越密集，一般采用默认值0.05. 该例的输出结果如下图所示：

2.参看资料

1.《C++ primer》 2.《The VTK User’s Guide – 11thEdition》 3.  张晓东, 罗火灵. VTK图形图像开发进阶[M]. 机械工业出版社, 2015.