小结：本博文主要讲解vtkPolyData接口及常用的方法实现原理。

vtkPolyData

1描述

vtkPolyData是一系列的数据集包括vertices，lines，polygons，triangle strips。

vtkPolyData是vtkDataSet的具体实现，代表了一系列的几何结构，包括vertices，lines，polygons，triangle strips，以及Point和Cell属性结构。

vtkPolyData支持的Cell类型为vtkVertex, vtkPolyVertex, vtkLine, vtkPolyLine, vtkTriangle, vtkQuad, vtkPolygon, and vtkTriangleStrip。

 

 

 注意：

1. vtkPolyData实现了代表0D的vertices，1D的Lines，2D的Polygons和TriangleStrips；因此vtkPolyData可以创建由混合单元格类型组成的vtkPolyData实例。由于接口的设计特性，vtkPolyData在插值时必须按顺序进行处理：按顶点（vtkVertex和vtkPolyVertex）的顺序，线（vtkLine和vtkPolyLine)，多边形(vtkTriangle，vtkQuad，vtkPolygon) 和 三角带（vtkTriangleStrip）。小伙伴可以参考vtkClipClosedSurface的具体实现来学习具体过程，附上相关博文链接：VTK中Clip/Trim总结_雪易的博客-CSDN博客

2. 在Filter的具体实现中，可能会将vtkTriangleStrip转换为vtkTriangles进行处理（vtkClipClosedSurface就是这么操作的）;也可能会将vtkDecimatePro转换为vtkTriangles或vtkTriangleStrip;

 2构建方法

#include <vtkActor.h>
#include <vtkCellArray.h>
#include <vtkNamedColors.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkPolygon.h>
#include <vtkProperty.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkSmartPointer.h>

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

  // Setup four points
  vtkSmartPointer<vtkPoints> points =
    vtkSmartPointer<vtkPoints>::New();
  points->InsertNextPoint(0.0, 0.0, 0.0);
  points->InsertNextPoint(1.0, 0.0, 0.0);
  points->InsertNextPoint(1.0, 1.0, 0.0);
  points->InsertNextPoint(0.0, 1.0, 0.0);
  
  // Create the polygon
  vtkSmartPointer<vtkPolygon> polygon =
    vtkSmartPointer<vtkPolygon>::New();
  polygon->GetPointIds()->SetNumberOfIds(4); //make a quad
  polygon->GetPointIds()->SetId(0, 0);
  polygon->GetPointIds()->SetId(1, 1);
  polygon->GetPointIds()->SetId(2, 2);
  polygon->GetPointIds()->SetId(3, 3);
  
  // Add the polygon to a list of polygons
  vtkSmartPointer<vtkCellArray> polygons =
    vtkSmartPointer<vtkCellArray>::New();
  polygons->InsertNextCell(polygon);

  // Create a PolyData
  vtkSmartPointer<vtkPolyData> polygonPolyData =
    vtkSmartPointer<vtkPolyData>::New();
  polygonPolyData->SetPoints(points);
  polygonPolyData->SetPolys(polygons);

  // Create a mapper and actor
  vtkSmartPointer<vtkPolyDataMapper> mapper =
    vtkSmartPointer<vtkPolyDataMapper>::New();
  mapper->SetInputData(polygonPolyData);

  vtkSmartPointer<vtkActor> actor =
    vtkSmartPointer<vtkActor>::New();
  actor->SetMapper(mapper);
  actor->GetProperty()->SetColor(
    colors->GetColor3d("Silver").GetData());

  // Visualize
  vtkSmartPointer<vtkRenderer> renderer =
    vtkSmartPointer<vtkRenderer>::New();
  vtkSmartPointer<vtkRenderWindow> renderWindow =
    vtkSmartPointer<vtkRenderWindow>::New();
  renderWindow->SetWindowName("Polygon");
  renderWindow->AddRenderer(renderer);
  vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
    vtkSmartPointer<vtkRenderWindowInteractor>::New();
  renderWindowInteractor->SetRenderWindow(renderWindow);

  renderer->AddActor(actor);
  renderer->SetBackground(colors->GetColor3d("Salmon").GetData());
  renderWindow->Render();
  renderWindowInteractor->Start();

  return EXIT_SUCCESS;
}

3涉及的方法

1）GetCellNeighbors-获取指定Cell，指定点的相邻Cell

   /**
   * Get the neighbors at an edge. More efficient than the general
   * GetCellNeighbors(). Assumes links have been built (with BuildLinks()),
   * and looks specifically for edge neighbors.
   */
  void GetCellEdgeNeighbors(vtkIdType cellId, vtkIdType p1, vtkIdType p2, vtkIdList* cellIds);

2）获取PolyData的全部内容

vtkPolyData* pd = ...

//获取pd中的点
vtkPoints* inPts = pd->GetPoints();
vtkIdType numPts = pd->GetNumberOfPoints();

//获取pd中所有的Cells，包括vertex,line,poly,strip
vtkCellArray* vertexs = pd->GetVerts();
vtkCellArray* lines = pd->GetLines();
vtkCellArray* polys = pd->GetPolys();
vtkCellArray* strips = pd->GetStrips();
vtkIdType numVertexs = pd->GetNumberOfVerts();
vtkIdType numLines = pd->GetNumberOfLines();
vtkIdType numPolys = pd->GetNumberOfPolys();
vtkIdType numStrips = pd->GetNumberOfStrips();

//numcells = numVertexs+numLines+numPolys+numStrips
vtkIdType numCells = pd->GetNumberOfCells();

vtkPolyData* pd = ...
vtkIdType cellId;
vtkIdType numCells = pd->GetNumberOfCells();
vtkGenericCell* cell;
vtkPoints* cellPts;
vtkIdList* cellIds;
for (cellId = 0; cellId < numCells; cellId++)
{
  pd->GetCell(cellId, cell);
  cellPts = cell->GetPoints();
  cellIds = cell->GetPointIds();
}

 

3) vtkPolyData->vtkUnstructuredGrid

vtkUnstructuredGrid* uGrid = vtkUnstructuredGrid::New();
uGrid->SetPoints(inPts);

const vtkIdType* pts = nullptr;
vtkIdType npts;
for (vtkIdType id = 0; id < numCells; id++)
{
	pd->GetCellPoints(id, npts, pts);
	uGrid->InsertNextCell(pd->GetCellType(id), npts, pts);
}