【点云处理技术之PCL】滤波器——直通滤波器(pcl::PassThrough)

直通滤波器，是直接根据滤波器设定的条件，选择自己所需点云。可以选择保留设定范围内的点云，也可以选择滤除设定范围内的点云，保留或者滤出是由setFilterLimitsNegative进行模式开关的。

代码中，设定z轴的条件，保留z方向范围[0,1]内的点。

#include <iostream>
#include <pcl/point_types.h>
#include <pcl/filters/passthrough.h>

int main(int argc, char **argv)
{
    pcl::PointCloud<pcl::PointXYZ>::Ptr cloud(new pcl::PointCloud<pcl::PointXYZ>);
    pcl::PointCloud<pcl::PointXYZ>::Ptr cloud_filtered(new pcl::PointCloud<pcl::PointXYZ>);

    // Fill in the cloud data
    cloud->width = 5;
    cloud->height = 1;
    cloud->points.resize(cloud->width * cloud->height);

    for (auto &point : *cloud) //填充点云
    {
        point.x = 1024 * rand() / (RAND_MAX + 1.0f);
        point.y = 1024 * rand() / (RAND_MAX + 1.0f);
        point.z = 1024 * rand() / (RAND_MAX + 1.0f);
    }
    cloud->points[0].z = 1;//为了测试边界条件
    cloud->points[1].z = 0;

    std::cerr << "Cloud before filtering: " << std::endl;
    for (const auto &point : *cloud)
        std::cerr << "    " << point.x << " "
                  << point.y << " "
                  << point.z << std::endl;

    // Create the filtering object
    //设置滤波器对象
    pcl::PassThrough<pcl::PointXYZ> pass;
    pass.setInputCloud(cloud);    //输入点云
    pass.setFilterFieldName("z"); //滤波字段
    //这里只保留 0.0 < z < 1.0的点云
    pass.setFilterLimits(0.0, 1.0); //设置过滤字段的范围
    //setFilterLimitsNegative默认设置为false。如果设置true，则表示setFilterLimits范围内的点滤掉
    //pass.setFilterLimitsNegative (true);
    pass.filter(*cloud_filtered); //执行过滤，并输出到cloud_filtered，但是输入的cloud不会变化

    std::cerr << "Cloud before filtering:cloud " << std::endl;
    for (const auto &point : *cloud)
        std::cerr << "    " << point.x << " "
                  << point.y << " "
                  << point.z << std::endl;

    std::cerr << "Cloud after filtering: cloud_filtered" << std::endl;
    for (const auto &point : *cloud_filtered)
        std::cerr << "    " << point.x << " "
                  << point.y << " "
                  << point.z << std::endl;

    return (0);
}

输出结果如下，可以看到只保留了z值在[0,1]的范围。

Cloud before filtering: 
    0.352222 -0.151883 1
    -0.397406 -0.473106 0
    -0.731898 0.667105 0.441304
    -0.734766 0.854581 -0.0361733
    -0.4607 -0.277468 -0.916762
Cloud before filtering:cloud 
    0.352222 -0.151883 1
    -0.397406 -0.473106 0
    -0.731898 0.667105 0.441304
    -0.734766 0.854581 -0.0361733
    -0.4607 -0.277468 -0.916762
Cloud after filtering: cloud_filtered
    0.352222 -0.151883 1
    -0.397406 -0.473106 0
    -0.731898 0.667105 0.441304

参考：https://pcl.readthedocs.io/projects/tutorials/en/latest/passthrough.html#passthrough