VTK中图像像素位置的提取

当使用VTK对图像进行显示，图像像素点的提取是其中一个重要的应用，包括对像素位置的判断，以及对像素值的读取。

对像素点提取的思路包括三个步骤：

获取renderer的指针，然后使用picker类来获得点击的点。

			int *pos = this->GetInteractor()->GetEventPosition();
			this->picker->Pick( pos[0], pos[1], 0.0, imageViewer->GetRenderer() );
			double selectionPos[3];
			this->picker->GetPickPosition(selectionPos);

在求解pick位置的过程中，需要对其进行操作，以得到具体的位置。

			// Fixes some numerical problems with the picking
			double *bounds = this->imageViewer->GetImageActor()->GetDisplayBounds();
			//std::cout << bounds[4] << std::endl;
			int axis = this->imageViewer->GetSliceOrientation();
			selectionPos[axis] = bounds[2*axis];

对得到的位置进行插值，提取对应的像素值

      vtkPointData* pd = image->GetPointData();
      if( !pd )
        {
        return;
        }
 
      this->PointData->InterpolateAllocate( pd, 1, 1 );
 
      // Use tolerance as a function of size of source data
      double tol2 = image->GetLength();
      tol2 = tol2 ? tol2*tol2 / 1000.0 : 0.001;
 
      // Find the cell that contains pos
      int subId;
      double pcoords[3], weights[8];
      vtkCell* cell = image->FindAndGetCell(
          pos, NULL, -1, tol2, subId, pcoords, weights );
      if( cell )
        {
        // Interpolate the point data
        this->PointData->InterpolatePoint( pd, 0, cell->PointIds, weights );
        int components =
          this->PointData->GetScalars()->GetNumberOfComponents();
        double* tuple = this->PointData->GetScalars()->GetTuple( 0 );

参考文献：

• http://vtk.1045678.n5.nabble.com/help-on-how-to-get-the-pixel-position-td1224404.html

• http://www.vtk.org/Wiki/VTK/Examples/Cxx/Images/PickPixel
• http://www.vtk.org/Wiki/VTK/Examples/Cxx/Images/PickPixel2
• http://www.vtk.org/Wiki/VTK/Examples/Cxx/Picking/HighlightPickedActor