[ros-users] Bug in Point Cloud Library: MLESAC

[Radu Bogdan Rusu]

I don't recommend using MLESAC, RMSAC, or RRANSAC for solving the table_lms400 planarity model problem, at least not in 
their current form. All these methods are only useful in situations where most of the data samples belong to the model 
(80%+ for example), and a fast outlier rejection algorithm is needed. In the table_lms400 case, the model constitutes 
only roughly half of the scene, and that can cause problems. That's not to say that things couldn't be improved of 
course. Patches... welcome ;)

I would use RANSAC, LMEDS and MSAC for problems such as table_lms400, as they are more robust.

Cheers,
Radu.

On 07/27/2010 05:42 AM, PinakiBanerjee wrote:
>
> Hi, I tried using MLESAC for SACMODEL_PLANE for segmentation of point cloud
> dataset : table_scene_lms400.pcd from ROS. Unfortunately it fails to detect
> the planes as can be seen in the image. This is the result obtained for 2000
> iterations :
>
> http://ros-users.122217.n3.nabble.com/file/n999095/MLESAC_2000.png
>
> Color convention : Green: Plane 1, Red: Plane 2., White: Remaining pixels.
>
>
> Although the result of RANSAC for 50 iteration is accpetable as can be seen
> below:
>
> http://ros-users.122217.n3.nabble.com/file/n999095/RANSAC_50.png
>
>
> The code i used to prodece it is given below:
>
> #include "pcl/io/pcd_io.h"
> #include "pcl/point_types.h"
>
> #include "pcl/sample_consensus/method_types.h"
> #include "pcl/sample_consensus/model_types.h"
> #include "pcl/segmentation/sac_segmentation.h"
> #include "fstream"
>
> using namespace std;
>
> /* ---[ */
> int
>    main (int argc, char** argv)
> {
>
> //-----------------------Reading the data-----------------------------
> sensor_msgs::PointCloud2 cloud_blob;
>    pcl::PointCloud<pcl::PointXYZ>  cloud;
>
>    if (pcl::io::loadPCDFile ("table_scene_lms400.pcd", cloud_blob) == -1)
>    {
>      ROS_ERROR ("Couldn't read file test_pcd.pcd");
>      return (-1);
>    }
>    ROS_INFO ("Loaded %d data points from test_pcd.pcd with the following
> fields: %s", (int)(cloud_blob.width * cloud_blob.height), pcl::getFieldsList
> (cloud_blob).c_str ());
>
>   // Convert to the templated message type
>    point_cloud::fromMsg (cloud_blob, cloud);
>
>
> //-----------------------Appliying the segmentation
> algorithm-------------------------
>
>    pcl::ModelCoefficients coefficients;
>    pcl::PointIndices inliers;
>    // Create the segmentation object
>    pcl::SACSegmentation<pcl::PointXYZ>  seg;
>    // Optional
>    seg.setOptimizeCoefficients (true);
>    // Mandatory
>    seg.setModelType (pcl::SACMODEL_PLANE);
>    seg.setMethodType (pcl::SAC_MLESAC);
>    seg.setDistanceThreshold (0.01);
>    seg.setMaxIterations (2000);
>    seg.setInputCloud (boost::make_shared<pcl::PointCloud<pcl::PointXYZ>
>> (cloud));
>
> time_t tstart, tend;
>
> tstart = time(NULL);
>    seg.segment (inliers, coefficients);
> tend = time(NULL);
> ROS_INFO("Segmentation 1 Time elapsed %f", difftime(tend,tstart));
>
>    if (inliers.indices.size () == 0)
>    {
>      ROS_ERROR ("Could not estimate a planar model for the given dataset.");
>      return (-1);
>    }
> ROS_INFO ("Done segmentation of initial cloud");
>   ROS_INFO("No. of Inliers1 :  %d",inliers.indices.size ());
>
> //--------------------------writing the
> inliers------------------------------
>
>
> ofstream SaveFile("inliers1_table_MLESAC_2000.txt");
>
> for (size_t i = 0; i<  inliers.indices.size (); ++i){
> SaveFile<<  cloud.points[inliers.indices[i]].x<<  " "<<
> cloud.points[inliers.indices[i]].y<<  ""
> <<cloud.points[inliers.indices[i]].z<<  endl;
> }
>
> SaveFile.close();
>
> ROS_INFO ("Results of segmentation of initial cloud written");
>
> //---------------------------------------------------------------------------
>
> pcl::PointCloud<pcl::PointXYZ>  cloud1;
>
> cloud1.width = cloud.width - inliers.indices.size();
> cloud1.height = 1;
> cloud1.points.resize (cloud1.width * cloud1.height);
>
> int first,mid,last,val,key,index;
> int a = 0;
> for(index= 0 ; index<cloud.width; index++ ){
>
> val=-1;
> first=0;
> last =inliers.indices.size()-1;
> key=index;
>
>     while (first<= last) {
>         mid = (first + last) / 2;  // compute mid point.
>         if (key>  inliers.indices[mid])
>             first = mid + 1;  // repeat search in top half.
>         else if (key<  inliers.indices[mid])
>             last = mid - 1; // repeat search in bottom half.
>         else{		
>             val=0;     // found it. return position /////
> 	   break;
> 	}
>     }
>
> 	if(val==-1){
> 	
> 	cloud1.points[a].x = 	cloud.points[index].x;
> 	cloud1.points[a].y = 	cloud.points[index].y;
> 	cloud1.points[a].z = 	cloud.points[index].z;
> 	a++;
> 	}
> }
> cout<<  a<<  " =  "<<  cloud1.width;
> ROS_INFO ("Cloud2 created successfully");
>
> //--------------------------writing the modified
> cloud------------------------------
>
>
> ofstream SaveFile3("cloud2_table_MLESAC_2000.txt");
>
> for (size_t i = 0; i<  cloud1.width; ++i){
> SaveFile3<<  cloud.points[i].x<<  " "<<  cloud.points[i].y<<  ""
> <<cloud.points[i].z<<  endl;
> }
>
> SaveFile3.close();
>
> ROS_INFO ("cloud2 written");
>
>
> //-----------------------Appliying the segmentation algorithm on the
> modified cloud-------------------------
>
>
>
>
>    seg.setInputCloud (boost::make_shared<pcl::PointCloud<pcl::PointXYZ>
>> (cloud1));
>    pcl::PointIndices inliers1;
> 	
> tstart = time(0);
>    seg.segment (inliers1, coefficients);
> tend = time(0);
>
> ROS_INFO("Segmentation 2 Time elapsed %f", difftime(tend,tstart));
>
>    if (inliers1.indices.size () == 0)
>    {
>      ROS_ERROR ("Could not estimate a planar model for the given dataset.");
>      return (-1);
>    }
>
>   ROS_INFO("No. of Inliers2 :  %d",inliers1.indices.size ());
> ROS_INFO ("Cloud2 segmented successfully");
> //--------------------------writing the
> inliers------------------------------//
>
>
> ofstream SaveFile1("inliers2_table_MLESAC_2000.txt");
>
> for (size_t i = 0; i<  inliers1.indices.size (); ++i)
> SaveFile1<<  cloud1.points[inliers1.indices[i]].x<<  " "<<
> cloud1.points[inliers1.indices[i]].y<<  ""
> <<cloud1.points[inliers1.indices[i]].z<<  endl;
>
> SaveFile1.close();
>
> ROS_INFO ("Cloud2 written successfully");
> //---------------------------------------------------------------------------
>
>    return (0);
> }
> /* ]--- */
>
>
> Is it a bug in the program? or am i missing some thing? Please help.

-- 
| Radu Bogdan Rusu | http://rbrusu.com/