本文主要是介绍ros sensor_msgs::laserscan 数据格式及velodyne_laserscan.cpp文件解析,希望对大家解决编程问题提供一定的参考价值,需要的开发者们随着小编来一起学习吧!
laserscan数据格式如下(摘自wiki):
每个成员根据注释容易看出表示什么意思,强调一个容易理解错误的地方,ranges[]数组表示雷达旋转时,记录从angle_min到angle_max 角度范围内的距离数据,数组的大小并不是固定的360个,与激光雷达转速、方向角分辨有关,即以多少角度为间隔采集数据,也就是消息里面的angle_increment,(angle_max-angle_min) /angle_increment 即是数组的大小,序号从angle_min开始,即angle_min对应的序号为0,intensities[]与ranges对应,记录每个数据点的强度或者是激光雷达的反射率。
下面通过分析velodyne官方源码中的由pointCloud转为laserscan的文件 velodyne_laserscan.cpp为例,说明如何发布laserscan消息。在注释中说明,请依序看完代码。
// Copyright (C) 2018, 2019 Kevin Hallenbeck, Joshua Whitley
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#include <sensor_msgs/point_cloud2_iterator.h>namespace velodyne_laserscan
{VelodyneLaserScan::VelodyneLaserScan(ros::NodeHandle &nh, ros::NodeHandle &nh_priv) :nh_(nh), srv_(nh_priv), ring_count_(0)
{ros::SubscriberStatusCallback connect_cb = boost::bind(&VelodyneLaserScan::connectCb, this);// 注册并绑定收到pointcloud2消息的回调函数 pub_ = nh.advertise<sensor_msgs::LaserScan>("scan", 10, connect_cb, connect_cb);//声明发布的话题srv_.setCallback(boost::bind(&VelodyneLaserScan::reconfig, this, _1, _2));//动态配置参数的回调函数,当设置的参数改变时回调调用}void VelodyneLaserScan::connectCb()
{boost::lock_guard<boost::mutex> lock(connect_mutex_);if (!pub_.getNumSubscribers()){sub_.shutdown();}else if (!sub_){sub_ = nh_.subscribe("velodyne_points", 10, &VelodyneLaserScan::recvCallback, this);}
}//收到点云数据消息的回调实现,即转化数据并发布scan话题
void VelodyneLaserScan::recvCallback(const sensor_msgs::PointCloud2ConstPtr& msg)
{// Latch ring count// 一开始ring_count为零,有动态参数配置后或者第二次收到数据后,即可正常工作// 此块逻辑不够清晰if (!ring_count_){// Check for PointCloud2 field 'ring'// 检查点去数据中是否有激光ID值,如果没有,则此点云数据无效,不处理数据。bool found = false;for (size_t i = 0; i < msg->fields.size(); i++){if (msg->fields[i].datatype == sensor_msgs::PointField::UINT16){if (msg->fields[i].name == "ring"){found = true;break;}}}if (!found){ROS_ERROR("VelodyneLaserScan: Field 'ring' of type 'UINT16' not present in PointCloud2");return;}//再次检查ring的值,感觉没鸟用,废代码for (sensor_msgs::PointCloud2ConstIterator<uint16_t> it(*msg, "ring"); it != it.end(); ++it){const uint16_t ring = *it;if (ring + 1 > ring_count_){ring_count_ = ring + 1;}}if (ring_count_){ROS_INFO("VelodyneLaserScan: Latched ring count of %u", ring_count_);}else{ROS_ERROR("VelodyneLaserScan: Field 'ring' of type 'UINT16' not present in PointCloud2");return;}}// Select ring to use// 通过配置,获取需要抽取的激光ID,即需要取哪一条线(比如VLP16中抽第8号线)来发布scan, // 并且给ring_count_赋值uint16_t ring;if ((cfg_.ring < 0) || (cfg_.ring >= ring_count_)){// Default to ring closest to being level for each known sensorif (ring_count_ > 32){ring = 57; // HDL-64E}else if (ring_count_ > 16){ring = 23; // HDL-32E}else{ring = 8; // VLP-16}}else{ring = cfg_.ring;}//如果没有配置参数,则按默认的线来运行,VLP16的8号laser id 最接近水平ROS_INFO_ONCE("VelodyneLaserScan: Extracting ring %u", ring);// Load structure of PointCloud2//获取 PointCloud2 点云数据中x,y,z,强度,laserid的位置偏移,相当于数组索引//初始值为-1,当获取到后,变为相应位置的正数,判断是否存在int offset_x = -1;int offset_y = -1;int offset_z = -1;int offset_i = -1;int offset_r = -1;for (size_t i = 0; i < msg->fields.size(); i++){if (msg->fields[i].datatype == sensor_msgs::PointField::FLOAT32){if (msg->fields[i].name == "x"){offset_x = msg->fields[i].offset;}else if (msg->fields[i].name == "y"){offset_y = msg->fields[i].offset;}else if (msg->fields[i].name == "z"){offset_z = msg->fields[i].offset;}else if (msg->fields[i].name == "intensity"){offset_i = msg->fields[i].offset;}}else if (msg->fields[i].datatype == sensor_msgs::PointField::UINT16){if (msg->fields[i].name == "ring"){offset_r = msg->fields[i].offset;}}}// Construct LaserScan message// 是否存在x,y,z值,如果不存在就报错返回,如果存在就初始化/scan消息// 初始化信息就可以看出/scan消息的结构组成if ((offset_x >= 0) && (offset_y >= 0) && (offset_r >= 0)){// /scan 数据的精度,即range[]数组的大小,// size 是一圈对应的精度,因为angle_min,angle_max 在后面已经固定写死了// 因此size 是(pi-(-pi))/resolutionconst float RESOLUTION = std::abs(cfg_.resolution);const size_t SIZE = 2.0 * M_PI / RESOLUTION;sensor_msgs::LaserScanPtr scan(new sensor_msgs::LaserScan());scan->header = msg->header;//可以看到angle_increment 的值即为RESOLUTION scan->angle_increment = RESOLUTION;//从-pi 到 pi ,程序已经写死了scan->angle_min = -M_PI;scan->angle_max = M_PI;// 截取0 到 200 米范围的数据,已经超VLP16量程了,所有数据都有效scan->range_min = 0.0;scan->range_max = 200.0;scan->time_increment = 0.0;//按分辨率推出的,ranges的大小在此定义scan->ranges.resize(SIZE, INFINITY);// 标准的点云数据中各个数据的序号是有规律的,否则是不规则的数据// 然而两者处理方式一样的,此处区分意义不大 if ((offset_x == 0) &&(offset_y == 4) &&(offset_i % 4 == 0) &&(offset_r % 4 == 0)){scan->intensities.resize(SIZE);const size_t X = 0;const size_t Y = 1;const size_t I = offset_i / 4;const size_t R = offset_r / 4;for (sensor_msgs::PointCloud2ConstIterator<float> it(*msg, "x"); it != it.end(); ++it){const uint16_t r = *((const uint16_t*)(&it[R])); // ring// 对比laser id 是否与需要取的一致,如果不一致,则不更新range[]以及intensities[]if (r == ring){const float x = it[X]; // xconst float y = it[Y]; // yconst float i = it[I]; // intensity//求某一角度对应的序号,反正切值刚好是从-pi 到 pi//序号从angle_min开始升序,angle_min 为-pi,因此实际为:// bin=(atan2f(y,x)-angle_min)/angle_increment const int bin = (atan2f(y, x) + static_cast<float>(M_PI)) / RESOLUTION;if ((bin >= 0) && (bin < static_cast<int>(SIZE))){//range[] 的值是平面距离scan->ranges[bin] = sqrtf(x * x + y * y);scan->intensities[bin] = i;}}}}else{ROS_WARN_ONCE("VelodyneLaserScan: PointCloud2 fields in unexpected order. Using slower generic method.");if (offset_i >= 0){scan->intensities.resize(SIZE);sensor_msgs::PointCloud2ConstIterator<uint16_t> iter_r(*msg, "ring");sensor_msgs::PointCloud2ConstIterator<float> iter_x(*msg, "x");sensor_msgs::PointCloud2ConstIterator<float> iter_y(*msg, "y");sensor_msgs::PointCloud2ConstIterator<float> iter_i(*msg, "intensity");for ( ; iter_r != iter_r.end(); ++iter_x, ++iter_y, ++iter_r, ++iter_i){const uint16_t r = *iter_r; // ringif (r == ring){const float x = *iter_x; // xconst float y = *iter_y; // yconst float i = *iter_i; // intensity const int bin = (atan2f(y, x) + static_cast<float>(M_PI)) / RESOLUTION;if ((bin >= 0) && (bin < static_cast<int>(SIZE))){scan->ranges[bin] = sqrtf(x * x + y * y);scan->intensities[bin] = i;}}}}else{sensor_msgs::PointCloud2ConstIterator<uint16_t> iter_r(*msg, "ring");sensor_msgs::PointCloud2ConstIterator<float> iter_x(*msg, "x");sensor_msgs::PointCloud2ConstIterator<float> iter_y(*msg, "y");for (; iter_r != iter_r.end(); ++iter_x, ++iter_y, ++iter_r){const uint16_t r = *iter_r; // ringif (r == ring){const float x = *iter_x; // xconst float y = *iter_y; // yconst int bin = (atan2f(y, x) + static_cast<float>(M_PI)) / RESOLUTION;if ((bin >= 0) && (bin < static_cast<int>(SIZE))){scan->ranges[bin] = sqrtf(x * x + y * y);}}}}}//发布 消息pub_.publish(scan);}else{ROS_ERROR("VelodyneLaserScan: PointCloud2 missing one or more required fields! (x,y,ring)");}
}//动态参数回调,设置ring 以及revolution
void VelodyneLaserScan::reconfig(VelodyneLaserScanConfig& config, uint32_t level)
{cfg_ = config;
}} // namespace velodyne_laserscan
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