Method GetTransform

Filters/General/vtkIntersectionPolyDataFilter.cxx:1825–1886

}

int vtkIntersectionPolyDataFilter::Impl::GetTransform(vtkTransform* transform, vtkPoints* points)
{
  double zaxis[3] = { 0, 0, 1 };
  double rotationAxis[3], normal[3], center[3], rotationAngle;

  double pt0[3], pt1[3], pt2[3];
  points->GetPoint(0, pt0);
  points->GetPoint(1, pt1);
  points->GetPoint(2, pt2);
  vtkTriangle::ComputeNormal(pt0, pt1, pt2, normal);

  double dotZAxis = vtkMath::Dot(normal, zaxis);
  if (fabs(1.0 - dotZAxis) < 1e-6)
  {
    // Aligned with z-axis
    rotationAxis[0] = 1.0;
    rotationAxis[1] = 0.0;
    rotationAxis[2] = 0.0;
    rotationAngle = 0.0;
  }
  else if (fabs(1.0 + dotZAxis) < 1e-6)
  {
    // Co-linear with z-axis, but reversed sense.
    // Aligned with z-axis
    rotationAxis[0] = 1.0;
    rotationAxis[1] = 0.0;
    rotationAxis[2] = 0.0;
    rotationAngle = 180.0;
  }
  else
  {
    // The general case
    vtkMath::Cross(normal, zaxis, rotationAxis);
    vtkMath::Normalize(rotationAxis);
    double dot = vtkMath::Dot(zaxis, normal);
    if (dot > 1.0)
    {
      dot = 1.0;
    }
    else if (dot < -1.0)
    {
      dot = -1.0;
    }
    rotationAngle = vtkMath::DegreesFromRadians(acos(dot));
  }

  transform->PreMultiply();
  transform->Identity();

  transform->RotateWXYZ(rotationAngle, rotationAxis[0], rotationAxis[1], rotationAxis[2]);

  vtkTriangle::TriangleCenter(pt0, pt1, pt2, center);
  transform->Translate(-center[0], -center[1], -center[2]);

  int zaxisdotsign = 1;
  if (dotZAxis < 0)
  {
    zaxisdotsign = -1;