我想在 nifti 标签集上运行 vtkMarchingCubes。我要为其生成曲面的体素区域都具有相同的值。我有两个问题。首先，我似乎错误地设置了算法，因为生成的 vtkPolyData 显然没有顶点。其次，从 vtkOBJExporter 文档中我不清楚如何将 vtkPolyData 导出为波前 .OBJ 文件。如果有人看到下面的代码有任何问题，或者可以告诉我如何将 vtkPolyData 导出为 OBJ，我将不胜感激。
//Read The Nifti Label File
string input_path = "/MyPath/labels.nii";
nifti_image *im = nifti_image_read(input_path.c_str(),true);
cout<<im->nx<<","<<im->ny<<","<<im->nz<<endl; //Confirms Read Works
// Set up vtk image data
vtkImageImport* importer = vtkImageImport::New();
importer->SetImportVoidPointer((void*)im->data);
importer->SetDataScalarTypeToFloat();
importer->SetDataExtent(0, im->nx-1, 0, im->ny-1, 0, im->nz-1);
importer->SetWholeExtent(0, im->nx-1, 0, im->ny-1, 0, im->nz-1);
vtkImageData* point_cloud = importer->GetOutput();
point_cloud->SetScalarTypeToFloat();
point_cloud->SetExtent(0, im->nx-1, 0, im->ny-1, 0, im->nz-1);
point_cloud->SetSpacing(im->dx, im->dy, im->dz);
//Apply Threshold To Cut Out Other Data
//Is this needed or will Marching Cubes properly identify the region
vtkImageThreshold* threshold = vtkImageThreshold::New();
threshold->ThresholdBetween(label_number,label_number);
threshold->SetInValue(255);
threshold->SetOutValue(0);
threshold->SetInput(point_cloud);
//Apply the Marching Cubes algorithm
vtkMarchingCubes* marching_cubes = vtkMarchingCubes::New();
marching_cubes->SetValue(0, 127.0f);
marching_cubes->SetInput(threshold->GetOutput()); //(vtkDataObject*)point_cloud);
vtkPolyData* surface = marching_cubes->GetOutput();
marching_cubes->Update();
//See That Marching Cubes Worked
cout<<"# Vertices: "<< surface->GetNumberOfVerts()<<endl;
cout<<"# Cells: "<< surface->GetNumberOfCells()<<endl;
//Export (How is this done properly?)
vtkOBJExporter* exporter = vtkOBJExporter::New();
exporter->SetInput(vtkRenderWindow *renWin); //I don't want a render window, I want at file
exporter->SetFilePrefix("/MyPath/surface");
exporter->Write();