如何使用PCL从点云数据中提取一组点？

Question

我有一组点云数据，希望通过点击一个点来提取半径内的所有点。我还想把提取出的点放入到新的点云中。使用Pointpickingevent，我已经能够点击一个点并将其放入点云中。如何提取一组点，比如从所点击的点开始向外半径为0.02厘米的范围内的所有点，并将它们推入一个新的点云中？

- Username

Answer 1

给定一个点云：

pcl::PointCloud<pcl::PointXYZ>::Ptr cloud

然后生成Kdtree以执行高效的范围搜索：

pcl::KdTreeFLANN<pcl::PointXYZ> kdtree;
kdtree.setInputCloud (cloud);

接着，给定一个点和半径：

pcl::PointXYZ searchPoint(1,2,3);
float radius = 4;

您可以获取距离点 searchPoint radius 距离的所有点：

std::vector<int> pointIdxRadiusSearch; //to store index of surrounding points 
std::vector<float> pointRadiusSquaredDistance; // to store distance to surrounding points

if ( kdtree.radiusSearch (searchPoint, radius, pointIdxRadiusSearch, pointRadiusSquaredDistance) > 0 )
{
    for (size_t i = 0; i < pointIdxRadiusSearch.size (); ++i)
        std::cout << "    "  <<   cloud->points[ pointIdxRadiusSearch[i] ].x 
                << " " << cloud->points[ pointIdxRadiusSearch[i] ].y 
                << " " << cloud->points[ pointIdxRadiusSearch[i] ].z 
                << " (squared distance: " << pointRadiusSquaredDistance[i] << ")" << std::endl;
}

您可以打印出所有周围的点及其到搜索点的距离以检查代码的正确性。

最后，使用获取到的点创建云：

pcl::PointCloud<pcl::PointXYZ>::Ptr cloud_cluster (new pcl::PointCloud<pcl::PointXYZ>);
for (size_t i = 0; i < pointIdxRadiusSearch.size (); ++i)
    cloud_cluster->points.push_back(cloud->points[ pointIdxRadiusSearch[i] ]);
cloud_cluster->width = cloud_cluster->points.size ();
cloud_cluster->height = 1;
cloud_cluster->is_dense = true;

- Albert Pumarola

Answer 2

为了能够选择一个点，你可以类似于this answer使用PointPickingEvent。

在你的.h文件中的类声明，

class PCLViewer : public QMainWindow
{
  Q_OBJECT

public:
  explicit PCLViewer (QWidget *parent = 0);
  ~PCLViewer ();
    void pointPickCallback (const pcl::visualization::PointPickingEvent& event, void*);

public slots:

protected:
  boost::shared_ptr<pcl::visualization::PCLVisualizer> viewer;
  pcl::PointCloud<pcl::PointXYZRGB>::Ptr cloud;
  pcl::PointXYZ src_point_;
  bool src_point_selected_;

private:
  Ui::PCLViewer *ui;

};

在你的 .cpp 文件中，

PCLViewer::PCLViewer (QWidget *parent) :
  QMainWindow (parent),
  ui (new Ui::PCLViewer)
{
    ui->setupUi (this);

    [...]

    viewer.reset (new pcl::visualization::PCLVisualizer ("viewer", false));
    viewer->registerPointPickingCallback (&PCLViewer::pointPickCallback, *this);

    [...]
}

以及额外的功能，

void
PCLViewer::pointPickCallback (const pcl::visualization::PointPickingEvent& event, void*)
{
  // Check to see if we got a valid point. Early exit.
  int idx = event.getPointIndex ();
  if (idx == -1)
    return;

  // Get the point that was picked
  event.getPoint (src_point_.x, src_point_.y, src_point_.z);
  PCL_INFO ("Src Window: Clicked point %d with X:%f Y:%f Z:%f\n", idx, src_point_.x, src_point_.y, src_point_.z);
  src_point_selected_ = true;
}

在手动注册应用程序中，有一个更详细的示例，演示了它的利用方式： pcl/apps/src/manual_registration/manual_registration.cpp pcl/apps/include/pcl/apps/manual_registration.h

- R.Falque