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VTK-vtkSelectPolyDataFilter

news 来源：原创 2024/11/13 9:33:30

前言：本博文主要记录vtkSelectPolyDataFilter接口的应用，实现原理，以及与其近似的vtkClipPolyData&vtkImplicitSelectionLoop的应用相比较，帮助小伙伴理解vtkSelectPolyDataFilter接口的实现原理，并且与其它接口进行区分。

结果展示

    

                 SelectPolyData                                                  ImplicitSelectionLoop

vtkSelectPolyDataFilter

描述：vtkSelectPolyData是一个过滤器，它根据定义“循环”并指示循环内的区域来选择多边形数据。循环内的网格由完整的细胞组成(细胞没有被切割)。或者，此过滤器可用于生成标量。这些标量值是到循环的距离测量，可用于剪辑、等高线。或者提取数据(即隐式函数可以做的任何事情)。

循环由x-y-z点坐标数组定义。(坐标应与输入多边形数据在同一坐标空间中。)环可以是凹的，非平面的，但不能自相交。过滤器的输入是一个多边形网格(仅限曲面原语，如三角形条和多边形);输出是a)在选择循环GenerateSelectionScalarsOff内的原始网格铺设的一部分;或b)添加标量值的相同多边形网格(GenerateSelectionScalarsOn)。

算法工作原理如下:对于循环中的每个点坐标，网格中最近的点被找到。结果是一个由距离网格最近的点id组成的循环。然后，在网格中找到连接最近点的边缘(并沿着形成环路的线铺设)。贪心边跟踪过程如下所示。在当前点，选择方向为且端点离直线最近的网格边。沿着边缘走到新的终点，然后重复这个过程。这个过程一直持续到整个循环创建完成。

要确定网格的哪一部分在循环内部和外部，有三种可能的选择。1)最小连通区域，2)最大连通区域，3)最接近用户指定点的连通区域。(设置ivar SelectionMode)

一旦像上面那样计算循环，GenerateSelectionScalars将控制过滤器的输出。如果为on，则基于到环线的距离生成标量值。否则，将输出位于选择循环内的单元格。默认情况下，环路内的网格铺设为输出;然而，如果InsideOut打开了，那么在环路外的网格部分被输出。

过滤器可以配置为通过设置GenerateUnselectedOutput来生成网格的未选择部分作为输出。使用方法GetUnselectedOutput来访问此输出。(注意:这个标志只在enerateSelectionScalars关闭时才相关。)

实例TestSelectPolyData

#include <vtkSmartPointer.h>
#include <vtkProperty.h>
#include <vtkSelectPolyData.h>
#include <vtkSphereSource.h>
#include <vtkClipPolyData.h>
#include <vtkProperty.h>
#include <vtkPolyDataMapper.h>
#include <vtkLODActor.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderWindow.h>
#include <vtkRenderer.h>

#include <vtkNamedColors.h>

int main(int, char *[])
{
  
  vtkSmartPointer<vtkNamedColors> colors =
    vtkSmartPointer<vtkNamedColors>::New();

  vtkSmartPointer<vtkSphereSource> sphereSource = 
    vtkSmartPointer<vtkSphereSource>::New();
  sphereSource->SetPhiResolution(50);
  sphereSource->SetThetaResolution(100);
  sphereSource->Update();
      
  vtkSmartPointer<vtkPoints> selectionPoints =
    vtkSmartPointer<vtkPoints>::New();
    
  selectionPoints->InsertPoint( 0, -0.16553, 0.135971, 0.451972 );
  selectionPoints->InsertPoint( 1, -0.0880123, -0.134952, 0.4747);
  selectionPoints->InsertPoint( 2,  0.00292618, -0.134604, 0.482459 );
  selectionPoints->InsertPoint( 3, 0.0641941, 0.067112, 0.490947);
  selectionPoints->InsertPoint( 4, 0.15577, 0.0734765, 0.469245);
  selectionPoints->InsertPoint( 5, 0.166667, -0.129217, 0.454622 );
  selectionPoints->InsertPoint( 6, 0.241259, -0.123363, 0.420581);
  selectionPoints->InsertPoint( 7,  0.240334, 0.0727106, 0.432555);
  selectionPoints->InsertPoint( 8, 0.308529, 0.0844311, 0.384357 );
  selectionPoints->InsertPoint( 9, 0.32672, -0.121674, 0.359187);
  selectionPoints-> InsertPoint( 10, 0.380721, -0.117342, 0.302527);
  selectionPoints ->InsertPoint( 11, 0.387804, 0.0455074, 0.312375 );
  selectionPoints ->InsertPoint( 12, 0.43943, -0.111673, 0.211707);
  selectionPoints ->InsertPoint( 13, 0.470984, -0.0801913, 0.147919);
  selectionPoints ->InsertPoint( 14, 0.436777, 0.0688872, 0.233021 );
  selectionPoints ->InsertPoint( 15, 0.44874, 0.188852, 0.109882);
  selectionPoints ->InsertPoint( 16, 0.391352, 0.254285, 0.176943);
  selectionPoints ->InsertPoint( 17, 0.373274, 0.154162, 0.294296 );
  selectionPoints ->InsertPoint( 18, 0.274659, 0.311654, 0.276609);
  selectionPoints ->InsertPoint( 19, 0.206068, 0.31396, 0.329702);
  selectionPoints ->InsertPoint( 20, 0.263789, 0.174982, 0.387308 );
  selectionPoints ->InsertPoint( 21, 0.213034, 0.175485, 0.417142);
  selectionPoints ->InsertPoint( 22, 0.169113, 0.261974, 0.390286);
  selectionPoints ->InsertPoint( 23, 0.102552, 0.25997, 0.414814 );
  selectionPoints ->InsertPoint( 24, 0.131512, 0.161254, 0.454705);
  selectionPoints ->InsertPoint( 25, 0.000192443, 0.156264, 0.475307);
  selectionPoints ->InsertPoint( 26, -0.0392091, 0.000251724, 0.499943); 
  selectionPoints ->InsertPoint( 27, -0.096161, 0.159646, 0.46438 );
  
  vtkSmartPointer<vtkSelectPolyData> loop =
    vtkSmartPointer<vtkSelectPolyData>::New();
  loop->SetInputConnection(sphereSource->GetOutputPort());
  loop->SetLoop(selectionPoints);
  loop->GenerateSelectionScalarsOn();
  loop->SetSelectionModeToSmallestRegion(); //negative scalars inside
  
  vtkSmartPointer<vtkClipPolyData> clip = //clips out positive region
    vtkSmartPointer<vtkClipPolyData>::New();
  clip->SetInputConnection(loop->GetOutputPort());

  vtkSmartPointer<vtkPolyDataMapper> clipMapper = 
    vtkSmartPointer<vtkPolyDataMapper>::New();
  clipMapper->SetInputConnection(clip->GetOutputPort());
  clipMapper->ScalarVisibilityOff();

  vtkSmartPointer<vtkProperty> backProp =
    vtkSmartPointer<vtkProperty>::New();
  backProp->SetColor(colors->GetColor3d("tomato").GetData());

  vtkSmartPointer<vtkLODActor> clipActor = 
    vtkSmartPointer<vtkLODActor>::New();
  clipActor->SetMapper(clipMapper);
  clipActor->SetBackfaceProperty(backProp);
  clipActor->GetProperty()->SetColor(colors->GetColor3d("banana").GetData());

  vtkSmartPointer<vtkRenderer> renderer =
    vtkSmartPointer<vtkRenderer>::New();
    
  vtkSmartPointer<vtkRenderWindow> renderWindow =
    vtkSmartPointer<vtkRenderWindow>::New();
  renderWindow->AddRenderer(renderer);
  
  vtkSmartPointer<vtkRenderWindowInteractor> interactor =
    vtkSmartPointer<vtkRenderWindowInteractor>::New();
  interactor->SetRenderWindow(renderWindow);

  // Add the actors to the renderer, set the background and size
  renderer->AddActor (clipActor);
  renderer->SetBackground (colors->GetColor3d("slate_grey").GetData());

  renderWindow->SetSize (500, 500);

  renderWindow->Render();
  interactor->Start();


  return EXIT_SUCCESS;
}

实例2 ImplicitSelectionLoop

原理：采用vtkImplicitSelectionLoop作为vtkImplicitFunction，实现vtkClipPolyData分割，结果如上图ImplicitSelectionLoop所示。

#include <vtkClipPolyData.h>
#include <vtkImplicitSelectionLoop.h>
#include <vtkLODActor.h>
#include <vtkNamedColors.h>
#include <vtkPolyDataMapper.h>
#include <vtkProperty.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkSmartPointer.h>
#include <vtkSphereSource.h>

int main(int, char*[])
{

  auto colors = vtkSmartPointer<vtkNamedColors>::New();

  auto sphereSource = vtkSmartPointer<vtkSphereSource>::New();
  sphereSource->SetPhiResolution(100);
  sphereSource->SetThetaResolution(100);
  sphereSource->Update();

  auto selectionPoints = vtkSmartPointer<vtkPoints>::New();

  selectionPoints->InsertPoint(0, -0.16553, 0.135971, 0.451972);
  selectionPoints->InsertPoint(1, -0.0880123, -0.134952, 0.4747);
  selectionPoints->InsertPoint(2, 0.00292618, -0.134604, 0.482459);
  selectionPoints->InsertPoint(3, 0.0641941, 0.067112, 0.490947);
  selectionPoints->InsertPoint(4, 0.15577, 0.0734765, 0.469245);
  selectionPoints->InsertPoint(5, 0.166667, -0.129217, 0.454622);
  selectionPoints->InsertPoint(6, 0.241259, -0.123363, 0.420581);
  selectionPoints->InsertPoint(7, 0.240334, 0.0727106, 0.432555);
  selectionPoints->InsertPoint(8, 0.308529, 0.0844311, 0.384357);
  selectionPoints->InsertPoint(9, 0.32672, -0.121674, 0.359187);
  selectionPoints->InsertPoint(10, 0.380721, -0.117342, 0.302527);
  selectionPoints->InsertPoint(11, 0.387804, 0.0455074, 0.312375);
  selectionPoints->InsertPoint(12, 0.43943, -0.111673, 0.211707);
  selectionPoints->InsertPoint(13, 0.470984, -0.0801913, 0.147919);
  selectionPoints->InsertPoint(14, 0.436777, 0.0688872, 0.233021);
  selectionPoints->InsertPoint(15, 0.44874, 0.188852, 0.109882);
  selectionPoints->InsertPoint(16, 0.391352, 0.254285, 0.176943);
  selectionPoints->InsertPoint(17, 0.373274, 0.154162, 0.294296);
  selectionPoints->InsertPoint(18, 0.274659, 0.311654, 0.276609);
  selectionPoints->InsertPoint(19, 0.206068, 0.31396, 0.329702);
  selectionPoints->InsertPoint(20, 0.263789, 0.174982, 0.387308);
  selectionPoints->InsertPoint(21, 0.213034, 0.175485, 0.417142);
  selectionPoints->InsertPoint(22, 0.169113, 0.261974, 0.390286);
  selectionPoints->InsertPoint(23, 0.102552, 0.25997, 0.414814);
  selectionPoints->InsertPoint(24, 0.131512, 0.161254, 0.454705);
  selectionPoints->InsertPoint(25, 0.000192443, 0.156264, 0.475307);
  selectionPoints->InsertPoint(26, -0.0392091, 0.000251724, 0.499943);
  selectionPoints->InsertPoint(27, -0.096161, 0.159646, 0.46438);

  auto loop = vtkSmartPointer<vtkImplicitSelectionLoop>::New();
  loop->SetLoop(selectionPoints);

  auto clip = // clips out positive region
      vtkSmartPointer<vtkClipPolyData>::New();
  clip->SetInputConnection(sphereSource->GetOutputPort());
  clip->SetClipFunction(loop);
  clip->SetValue(0.0);

  auto clipMapper = vtkSmartPointer<vtkPolyDataMapper>::New();
  clipMapper->SetInputConnection(clip->GetOutputPort());
  clipMapper->ScalarVisibilityOff();

  auto backProp = vtkSmartPointer<vtkProperty>::New();
  backProp->SetColor(colors->GetColor3d("tomato").GetData());

  auto clipActor = vtkSmartPointer<vtkLODActor>::New();
  clipActor->SetMapper(clipMapper);
  clipActor->SetBackfaceProperty(backProp);
  clipActor->GetProperty()->SetColor(colors->GetColor3d("banana").GetData());

  auto renderer = vtkSmartPointer<vtkRenderer>::New();

  auto renderWindow = vtkSmartPointer<vtkRenderWindow>::New();
  renderWindow->AddRenderer(renderer);

  auto interactor = vtkSmartPointer<vtkRenderWindowInteractor>::New();
  interactor->SetRenderWindow(renderWindow);

  // Add the actors to the renderer, set the background and size
  renderer->AddActor(clipActor);
  renderer->SetBackground(colors->GetColor3d("slate_grey").GetData());

  renderWindow->SetSize(500, 500);

  renderWindow->Render();
  interactor->Start();

  return EXIT_SUCCESS;
}

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