Draw and refresh PCL pointclouds in QVTK widget

Question

My question concerns about PointClouds library (PCL) and QVTK widget.

I have an QVTK widget in a MainWindow widget. The method that draws my pointclouds is called each time I load a new pointcloud from disk (or a ToF camera):

void CamWindow::on_PointCloudChanged()
{
      //pclPointCloud is declared as "pcl::PointCloud<pcl::PointXYZ>::Ptr pclPointCloud;". When that variable is updated, this method is called.
      //pclVisorName is global std::string, with "visor" as content
      //pclPointCloudName is global std::string, with "MyPointCloud" as content
      pcl::visualization::PCLVisualizer localPclVisor = pcl::visualization::PCLVisualizer(pclVisorName,false);
      localPclVisor.addPointCloud<pcl::PointXYZ>(pclPointCloud,pclPointCloudName);
      //localPclVisor.setBackgroundColor(1,1,0);
      vtkSmartPointer<vtkRenderWindow> localRenderWindow = localPclVisor.getRenderWindow();
      ui->QvtkPointCloud->SetRenderWindow(localRenderWindow);
      ui->QvtkPointCloud->update();

    existPclPointCloud = true;
}

This works, but each time this method is called, the camera position, pointview and other things are reset. I want to change only pointcloud to view, without resetting positions, colors, etc. How can I achieve this?

I've tried things like:

std::string                         pclPointCloudName;
pcl::PointCloud<pcl::PointXYZ>::Ptr pclPointCloud;
pcl::visualization::PCLVisualizer   pclVisor;
std::string                         pclVisorName;
vtkSmartPointer<vtkRenderWindow>    renderWindow;

(declaring pointcloud representation components as global vars)

void CamWindow::on_PointCloudChanged()
{
      //pclPointCloud is declared as "pcl::PointCloud<pcl::PointXYZ>::Ptr pclPointCloud;". When that variable is updated, this method is called.
      //pclVisorName is global std::string, with "visor" as content
      //pclPointCloudName is global std::string, with "MyPointCloud" as content
    if (existPclPointCloud)
    {
        localPclVisor.updatePointCloud<pcl::PointXYZ>(pclPointCloud,pclPointCloudName);
    }
    else
    {
      pcl::visualization::PCLVisualizer pclVisor = pcl::visualization::PCLVisualizer(pclVisorName,false);
      pclVisor.addPointCloud<pcl::PointXYZ>(pclPointCloud,pclPointCloudName);
      vtkSmartPointer<vtkRenderWindow> renderWindow = pclVisor.getRenderWindow();
      ui->QvtkPointCloud->SetRenderWindow(renderWindow);        
    }
     ui->QvtkPointCloud->update();

    existPclPointCloud = true;
}

But this does not work... Declaring QVTK and PCL components as global variables (in MainWindow Widget) make this program to show nothing in QVTK widget!! Why?

[I've also tried several variations of this, but it appears as every PCL+VTK+QT variable must be local in method in order to work. Spent hours and hours looking and googling for docs about VTK Visualizer, QVTK methods, objects, etc with no luck]

I understand that vars and objects relatives to PCL+VTK+QT are never empty or null (as they're global in MainWindow!!)...

My environment is Ubuntu 12.04 LTS, with Qt Creator 2.5.2, 64 bits. PCL 1.6, VTK 5.8

Fei Fei · Accepted Answer · 2013-07-22T11:34:13

If I understood your implementation right, every time you want to update your point cloud (pc), you call CamWindow::on_PointCloudChanged() and a new pcl::visualization::PCLVisualizer gets initialized, that's why you lose all your camera settings.

Maybe this can help. Declare the visualizer as global var, outside of any method

pcl::visualization::PCLVisualizer pclVisor ("visor", false);

Then write an init method similar to this, which you have to call once at the beginning:

void CamWindow::init() {
   vtkSmartPointer<vtkRenderWindow> renderWindow = pclVisor.getRenderWindow();
   this->SetRenderWindow(renderWindow);

   this->show();
   this->update();
}

Now you can update the pc named cloud0, every time a new_pc was created:

void CamWindow::on_PointCloudChanged(pcl::PointCloud<pcl::PointXYZ>::Ptr new_pc) {
   if (!pc->empty()) {

      // in case there is no pc called `cloud0` - create one,
      // otherwise just update it
      if (!pclVisor.updatePointCloud<pcl::PointXYZ>(new_pc, "cloud0")) {
         pclVisor.addPointCloud<pcl::PointXYZ>(new_pc, "cloud0");
      } else {
         pclVisor.updatePointCloud<pcl::PointXYZ>(new_pc, "cloud0");
      } 

      this->update();
   } else {
      std::cerr << "There is nothing to add to the visualizer!" << std::endl;
   }
}

I haven't compiled the code, so feel free to edit my answer, in case you used it and found any mistake. But this should be the basic idea.

Draw and refresh PCL pointclouds in QVTK widget

1 Answers