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前言

本文分享VTK基础操作技术，记录vtk编程中常用的接口，变量等的创建及使用方法希望对各位小伙伴有所帮助！

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目录

前言

 1. vtkDoubleArray参数的创建

2. 已知方向v1，v2，计算法向量n

3. 计算点到有限直线的距离

4. 计算vtkPolygon的法线

5. vtkPlaneCollection的声明和遍历

6. 遍历不同类型的Cell

7. 三角形条带生成三角形规则

8. 实体与Surface的区别

9. vtkPriorityQueue 优先队列

10. 计算polygon的面积

11. vtkPolyData->vtkActor & vtkActor->vtkPolyData变换过程

12. 打印Print信息

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 1. vtkDoubleArray参数的创建

//代码摘自vtkPolyPlane的ComputeNormal函数中
const vtkIdType = 5;
vtkDoubleArray* Normals = vtkDoubleArray::New();
Normals->SetNumberOfComponents(3);
Normals->Allocate(3 * nLines);
Normals->SetName("Normals");
Normals->SetNumberOfTuples(nLines);

2. 已知方向v1，v2，计算法向量n

vtkMath::Cross(v1, v2, n);
vtkMath::Normalize(n);

3. 计算点到有限直线的距离

// Compute distance to finite line. Returns parametric coordinate t
// and point location on line.
double vtkLine::DistanceToLine(
  const double x[3], const double p1[3], const double p2[3], double& t, double closestPoint[3])
{
  const double* closest = nullptr;
  //
  //   Determine appropriate vectors
  //    计算P21向量
  double p21[3] = { p2[0] - p1[0], p2[1] - p1[1], p2[2] - p1[2] };

  //
  //   Get parametric location
  //    计算x点到P21为法向量的平面的距离
  double num = p21[0] * (x[0] - p1[0]) + p21[1] * (x[1] - p1[1]) + p21[2] * (x[2] - p1[2]);
  if (num == 0.0)
  {
    //若距离为0表示，x与p1点重合
    t = 0;
    closest = p1;
  }
  else
  {
    //计算p21点到p21为法向量的平面的距离
    double denom = vtkMath::Dot(p21, p21);

    // trying to avoid an expensive fabs
    double tolerance = VTK_TOL * num;//计算误差
    if (tolerance < 0.0)
    {
      tolerance = -tolerance;
    }
    if (denom < tolerance) // numerically bad!
    {
    //若p21点到平面的距离小于误差，若num>0,表示最近点为p2;反之为p1
      if (num > 0)
      {
        closest = p2;
        t = VTK_DOUBLE_MAX;
      }
      else
      {
        closest = p1;
        t = VTK_DOUBLE_MIN;
      }
    }
    //
    // If parametric coordinate is within 0<=p<=1, then the point is closest to
    // the line.  Otherwise, it's closest to a point at the end of the line.
    //
    else if ((t = num / denom) < 0.0)
    {
    //若x点与p21点的方向不一致，则最近点为p1
      closest = p1;
    }
    else if (t > 1.0)
    {
      closest = p2;
    }
    else
    {
      closest = p21;
      p21[0] = p1[0] + t * p21[0];
      p21[1] = p1[1] + t * p21[1];
      p21[2] = p1[2] + t * p21[2];
    }
  }

    //计算x到直线Line12的最近点。
  if (closestPoint)
  {
    closestPoint[0] = closest[0];
    closestPoint[1] = closest[1];
    closestPoint[2] = closest[2];
  }
    //返回x与最近点的距离的平方
  return vtkMath::Distance2BetweenPoints(closest, x);
}

4. 计算vtkPolygon的法线

void vtkPolygon::ComputeNormal(vtkPoints* p, int numPts, const vtkIdType* pts, double* n)
{
  int i;
  double v[3][3], *v0 = v[0], *v1 = v[1], *v2 = v[2], *tmp;
  double ax, ay, az, bx, by, bz;
  //
  // Check for special triangle case. Saves extra work.
  //
  n[0] = n[1] = n[2] = 0.0;
  if (numPts < 3)
  {
    return;
  }

  if (numPts == 3)
  {
    if (pts)
    {
      p->GetPoint(pts[0], v0);
      p->GetPoint(pts[1], v1);
      p->GetPoint(pts[2], v2);
    }
    else
    {
      p->GetPoint(0, v0);
      p->GetPoint(1, v1);
      p->GetPoint(2, v2);
    }
    vtkTriangle::ComputeNormal(v0, v1, v2, n);
    return;
  }

  //  Because polygon may be concave, need to accumulate cross products to
  //  determine true normal.
  //

  // set things up for loop
  if (pts)
  {
    p->GetPoint(pts[0], v1);
    p->GetPoint(pts[1], v2);
  }
  else
  {
    p->GetPoint(0, v1);
    p->GetPoint(1, v2);
  }

  for (i = 0; i < numPts; i++)
  {
    tmp = v0;
    v0 = v1;
    v1 = v2;
    v2 = tmp;

    if (pts)
    {
      p->GetPoint(pts[(i + 2) % numPts], v2);
    }
    else
    {
      p->GetPoint((i + 2) % numPts, v2);
    }

    // order is important!!! to maintain consistency with polygon vertex order
    ax = v2[0] - v1[0];
    ay = v2[1] - v1[1];
    az = v2[2] - v1[2];
    bx = v0[0] - v1[0];
    by = v0[1] - v1[1];
    bz = v0[2] - v1[2];

    n[0] += (ay * bz - az * by);
    n[1] += (az * bx - ax * bz);
    n[2] += (ax * by - ay * bx);
  }

  vtkMath::Normalize(n);
}

5. vtkPlaneCollection的声明和遍历

vtkNew<vtkPlaneCollection> planes;
vtkNew<vtkPlane> plane;
plane->SetOrigin(origin);
plane->SetNormal(normal);
planes->AddItem(plane);

vtkCollectionSimpleIterator iter;
int numPlanes = 0;
if(planes)
{
    planes->InitTraversal(iter);
    numPlanes = planes->GetNumberOfItems();
    vtkPlane* plane = nullptr;
    for (int planeId = 0; planes && (plane = planes->GetNextPlane(iter)); planeId++)
    {
        //plane 操作
    }
}

6. 遍历不同类型的Cell

vtkPolyData* inputDS = ...
vtkCellArray* inputPolys = inputDS->GetPolys();

const vtkIdType* pts = nullptr;
vtkIdType cellId, npts;
for(cellId = 0, inputPolys->InitTraversal(); inputPolys->GetNextCell(npts, pts); cellId++)
{
    ...
}

vtkCellArray *inVerts = input->GetVerts();
for (inVerts = input->GetVerts(), inVerts->InitTraversal(); inVerts->GetNextCell(npts, pts);)
{
    for (j = 0; j < npts; j++)
    {
      Verts[pts[j]].type = VTK_FIXED_VERTEX;
    }
}
  

  // 同理对于Line

7. 三角形条带生成三角形规则

vtkCellArray* strips = vtkCellArray::New();
strips->InsertNextCell(4);
strips->InsertCellPoint(0);
strips->InsertCellPoint(1);
strips->InsertCellPoint(3);
strips->InsertCellPoint(2);

生成的三角形为（0，1，3）和（3，1，2）。

8. 实体与Surface的区别

实体的所有Triangle的方向均指向内部。

9. vtkPriorityQueue 优先队列

vtkPriorityQueue* leftmostPoints = vtkPriorityQueue::New();
leftmostPoints->Allocate(8);
leftmostPoints->Insert(-10, 0);
leftmostPoints->Insert(10, 1);
leftmostPoints->Insert(-3, 2);
leftmostPoints->Insert(0, 3);
leftmostPoints->Insert(2, 4);
leftmostPoints->Insert(5, 5);
leftmostPoints->Insert(-80, 6);
leftmostPoints->Insert(30, 7);
while (leftmostPoints->GetNumberOfItems())
{
    vtkIdType currentPointID = leftmostPoints->Pop();
//currentPointID分别为6，0，2，3，4，5，1，7
}

10. 计算polygon的面积

vtkSphere::ComputeBoundingSphere(
  static_cast<vtkDoubleArray*>(polygon->Points->GetData())->GetPointer(0),
  polygon->PointIds->GetNumberOfIds(), sphere, hints);
//if (sphere[3] <= this->HoleSize)
//sphere[3]为polygon的面积

11. vtkPolyData->vtkActor & vtkActor->vtkPolyData变换过程

vtkPolyData* pd = ...;
vtkPolyDataMapper* mapper = vtkPolyDataMapper::New();
mapper->setInputData(pd);
vtkActor* actor = vtkActor::New();
actor->setMapper(mapper);

//vtkPolyData改变驱动vtkActor改变
pd->Modified(); //关联的Actor会自动更新

//vtkActor改变（发生移动或旋转等）,并不会驱动关联的PolyData数据进行改变
//1. 获取vtkActor变换矩阵
//2. 将变换矩阵作用于关联的PolyData对象即可。

12. 打印Print信息

vtkPolyData* pd;
pd->Print(std::cout)

感谢各位小伙伴的点赞+关注，小易会继续努力分享，一起进步！

你的赞赏是我的最最最最大的动力(＾Ｕ＾)ノ~ＹＯ