Ground Removal

Sliding Window’s method

1. push all data into a 0.1×0.1×0.1 $m^3$ per cell
   1. sub item one
   2. sub item two
   3. sub item three
2. sort cells from high to low
3. use sliding window with hight threshold
   1. compute height difference of this cell
   2. also consider neighbour cells

plane point ransac filter

1. choose approximate ground data
2. use PCL’s ransac segmentation model

    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_PLANE);
    seg.setMethodType (pcl::SAC_RANSAC);
    seg.setDistanceThreshold (0.01);

    seg.setInputCloud (cloud);
    seg.segment (*inliers, *coefficients);

tricks 1

  for one frame lidar data, we may choose the downside lidar(the red curve), this will save a lot of time.

tricks 2

    seg.setDistanceThreshold( 0.05 );
    seg.setAxis( axis );
    seg.setEpsAngle( pcl::deg2rad( 10.0 ) );

  the plane may vertical to vector(0,0,1), so we’d better to set axix to be (0,0,1) as well as the Eps angle.

tricks 3

  what if we may encounter two planes, like this:

  and if this time it’s not good we may seg it again(with last time’s coeef),Its interface is like this:

    void seg_ground_cloud( pcl::ModelCoefficients::Ptr& coefficients,
                          Eigen::Vector3f& axis,
                          int threshold = 0.05 );

plane point angle_method1

we have one frame data like this: for every column,data like this: we use this stratege, like this: if the angle we get is above threshold, we think it’s not ground point, and cotinue.And main precedure is under below:

plane point angle_method1

main difference: not only consider vertical angle, but also horizontal angle .The author use BFS method to compute which are ground points, the algorithm is like this:

ref: PRBonn/depth_clustering