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Fitting line to pointcloud data

asked 2015-01-08 18:19:40 -0600

metal gravatar image

Hello Everyone, I am trying to fit a line to a point-cloud data received from a 2D lidar.

I am using random sample consus from pcl library to get this done. The first picture when the LIDAR is aligned with the wall, the line fits well. But when lidar is yawed the line deviates by certain degrees.

image description image description

Here is the code which does it:

 ros::Publisher marker_pub;
ros::Publisher pub;
ros::Publisher pub1;
visualization_msgs::Marker marker;
visualization_msgs::Marker text_1;
#define PI 3.14159265
using namespace std; 
float angle=0.0;
std::ostringstream tostr;
#include <sstream>    
void cloud_cb (const pcl::PCLPointCloud2ConstPtr& input)
        pcl::PCLPointCloud2::Ptr cloud_filtered (new pcl::PCLPointCloud2);
    pcl::PassThrough<pcl::PCLPointCloud2> pass_through_x;
        pcl::PassThrough<pcl::PCLPointCloud2> pass_through_y;

    // set fieldname we want to filter over
    pass_through_x.setFilterFieldName ("x");
    // set range for selected field to 1.0 - 1.5 meters
    pass_through_x.setFilterLimits (0.0,1.0);
    // do filtering
    pass_through_x.filter (*cloud_filtered);

    pass_through_y.setInputCloud (cloud_filtered);
    // set fieldname we want to filter over
    pass_through_y.setFilterFieldName ("y");
    // set range for selected field to 1.0 - 1.5 meters
    pass_through_y.setFilterLimits (0.0, 2.0);
    // do filtering
    pass_through_y.filter (*cloud_filtered); 

    pcl::PointCloud< pcl::PointXYZ> cloud;
        pcl::fromPCLPointCloud2(*cloud_filtered, cloud);
        pcl::ModelCoefficients::Ptr coefficients (new pcl::ModelCoefficients);
    pcl::PointIndices::Ptr inliers (new pcl::PointIndices);
    // Create the segmentation object
    pcl::SACSegmentation<pcl::PointXYZ> seg;
    // Optional
    seg.setOptimizeCoefficients (true);
    // Mandatory
    seg.setModelType (pcl::SACMODEL_LINE);
    seg.setMethodType (pcl::SAC_RANSAC);
    seg.setDistanceThreshold (0.006);
    seg.setInputCloud (cloud.makeShared ());
    seg.segment (*inliers, *coefficients);

    if (inliers->indices.size () == 0)
    PCL_ERROR ("Could not estimate a LINE model for the given dataset.");
        angle=2*asin(coefficients->values[4])*180.0/PI;//formulae for quarternions.
    //std::cerr <<"deviation from the wall:"<<angle<<endl;

    tostr << angle; 
    text_1.ns = "vehicle_orientation";
    text_1.header.frame_id = "laser";
    text_1.header.stamp = ros::Time::now();
    text_1.type = visualization_msgs::Marker::TEXT_VIEW_FACING;
        text_1.action = visualization_msgs::Marker::ADD;
        text_1.pose.position.x =0.0;// coefficients->values[0];
        text_1.pose.position.y =-0.3;// coefficients->values[1];
        text_1.pose.position.z =0.0;// coefficients->values[2];
        text_1.pose.orientation.x = 0.0;
        text_1.pose.orientation.y = 0.0;
        text_1.pose.orientation.z = 0.0;
        text_1.pose.orientation.w = 1.0; = 1;

        text_1.scale.z = 0.12;
        text_1.color.r = 0.0f;
        text_1.color.g = 1.0f;
        text_1.color.b = 0.0f;
        text_1.color.a = 1.0f;
        text_1.lifetime = ros::Duration();

              marker.ns = "vehicle_orientation";
             marker.header.frame_id = "laser";
             marker.header.stamp = ros::Time::now();
             marker.type = visualization_msgs::Marker::ARROW;
            marker.action = visualization_msgs::Marker::ADD;
        marker.pose.position.x = coefficients->values[0];
        marker.pose.position.y = coefficients->values[1];
        marker.pose.position.z = coefficients->values[2];
        marker.pose.orientation.x = coefficients->values[3];
        marker.pose.orientation.y = coefficients->values[4];
        marker.pose.orientation.z = coefficients->values[5];
        marker.pose.orientation.w = 0.0; = 0;
        marker.scale.x = 0.6;
        marker.scale.y = 0.01;
        marker.scale.z = 0.01;
        // Set the color -- be sure to set alpha to something ...
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2 Answers

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answered 2015-03-05 13:16:52 -0600

metal gravatar image

It works now!!. I was visualizing it wrongly. The trick is to take the rotation coefficients and convert it into quaternions, which is what RVIZ understands.

Here is the modified code snippet which does that:

        tf::Vector3 axis_vector(coefficients->values[3], coefficients->values[4], coefficients->values[5]);
        tf::Vector3 up_vector(1.0, 0.0, 0.0);
        tf::Vector3 right_vector = axis_vector.cross(up_vector);//
        tf::Quaternion q(right_vector, -1.0*acos(;//
        geometry_msgs::Quaternion line_orientation;
        tf::quaternionTFToMsg(q, line_orientation);

Screenshot from 2015-03-05 13:09:42.png Screenshot from 2015-03-05 13:09:48.png

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hey, nice work.

did you open the source code on the github or the whole code opened yet?

joeaaron gravatar image joeaaron  ( 2019-01-26 20:21:22 -0600 )edit

answered 2015-02-11 05:15:01 -0600

The line coefficients are x, y, z, dx, dy, dz, not pose.

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Asked: 2015-01-08 18:19:40 -0600

Seen: 4,852 times

Last updated: Mar 05 '15