rosbag 使用心得

比较完整的rosbag指令介绍：ROS-wiki

下面写一些我遇到的问题及解决方案：

问题1：

rosbag record -o /home/inin/data/ /occam/image_tiles0 /occam/stitched_image0

我在执行以上指令 录包时会出现丢包的现象，结果如下：

inin@inin:~$ rosbag record -o /home/inin/data/ /occam/image_tiles0 /occam/stitched_image0
[ INFO] [1554260232.649125239]: Subscribing to /occam/image_tiles0
[ INFO] [1554260232.651262266]: Subscribing to /occam/stitched_image0
[ INFO] [1554260232.653578956]: Recording to /home/inin/data/_2019-04-03-10-57-12.bag.
[ WARN] [1554260241.161152134]: rosbag record buffer exceeded.  Dropping oldest queued message.

原因在于我记录的是原始图像，非常大（10s=5g）而rosbag的缓存空间与磁盘写入带宽有限，因此可以从两方面着手。

解决方案1：

法1.提高rosbag的缓存空间：

rosbag record -o /home/inin/data/ -b 4096 /occam/stitched_image0 /occam/image_tiles0

 指令如上所示，rosbag 中加入-b num ,即为将缓存空间设置成num大小，在ROS-wiki也有说明。

 play之后可视化可用：

rosrun image_view image_view image:=/occam/image_tiles0

ros订阅：

class Images
{
public:image_transport::Subscriber sub_image;theseImages(){ros::NodeHandle node;image_transport::ImageTransport it(node);sub_image = it.subscribe("/usb_cam/image_raw", 1, &Images::imageCallback, this);}void imageCallback(const sensor_msgs::ImageConstPtr& msg){try{cv::imshow("view", cv_bridge::toCvShare(msg, "bgr8")->image);cv::waitKey(30);}catch (cv_bridge::Exception& e){ROS_ERROR("Could not convert from '%s' to 'bgr8'.", msg->encoding.c_str());}}
};int main(int argc, char **argv)
{ros::init(argc, argv, "my_node");ROS_INFO("my_node running...");Images images;ros::spin();return 0;
}

法2.压缩原始图像大小

rosbag record -o /home/inin/data/ /occam/stitched_image0/compressed /occam/image_tiles0/compressed

存储图像的压缩格式/compressed,可有效减小数据写入大小(1min=1G)，然而压缩后的图像是一种有损压缩对图像质量要求极高的情况慎用，当然一般做视觉计算是无所谓的，相当于把raw格式的图片转换为jpeg格式。

在可视化时指令也有所改变：

rosrun image_view image_view image:=/occam/image_tiles0 compressed

针对压缩图像的ros定义节点可以参考以下：

#include <ros/ros.h>
#include <opencv2/highgui/highgui.hpp>
#include <cv_bridge/cv_bridge.h>void imageCallback(const sensor_msgs::CompressedImageConstPtr& msg)
{try{cv::Mat image = cv::imdecode(cv::Mat(msg->data),1);//convert compressed image data to cv::Matcv::imshow("view", image);cv::waitKey(10);}catch (cv_bridge::Exception& e){ROS_ERROR("Could not convert to image!");}
}int main(int argc, char **argv)
{ros::init(argc, argv, "image_listener");ros::NodeHandle nh;cv::namedWindow("view");cv::startWindowThread();ros::Subscriber sub = nh.subscribe("/usb_cam/image_raw/compressed", 1, imageCallback);ros::spin();cv::destroyWindow("view");
}

问题2：

从一个包含众多ｔｏｐｉｃ的rosbag中分离出我想要的topic:

rosbag filter 2000-01-07-01-07-03.bag split/only-tiles.bag "topic == '/occam/image_tiles0/compressed /InsInfo'"