How to extract a set of points in a point cloud data using PCL? - point-cloud-library

Question

I have a point cloud data, where by clicking a point, I want to extract points surrounding the clicked point within a radius. I want to also push the extracted points into a new cloud. Using Pointpickingevent, I am able to click one point and push it into the cloud. How do I extract a set of points, say points surrounding 0.02cm radius from the clicked point and push them into a new cloud?

Answer 1

Given a point cloud:
pcl::PointCloud<pcl::PointXYZ>::Ptr cloud
A Kdtree is then generated to perform an efficient range search:
pcl::KdTreeFLANN<pcl::PointXYZ> kdtree;
kdtree.setInputCloud (cloud);
Then, given a point and a radius:
pcl::PointXYZ searchPoint(1,2,3);
float radius = 4;
You can get all the points that are at a distance radius from the point searchPoint:
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;
}
You can print all the surrounding points and their distance to the searchPoint to check the code functional correctness.
Finally, create a cloud with the obtained points:
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;

Answer 2

In order to be able to pick a point you can use PointPickingEvent similarly to this answer.
The Class declaration in your .h,
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;
};
In your .cpp,
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);
[...]
}
and the additional function,
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;
}
There is a more detailed example of the utilisation of it in the manual registration app:
pcl/apps/src/manual_registration/manual_registration.cpp
pcl/apps/include/pcl/apps/manual_registration.h