git init
git add README.md
git commit -m "first commit"
git remote add origin https://github.com/mengxingshifen1218/pcl-learn.git
git push -u origin master
rosrun pcl_ros bag_to_pcd <input_file.bag> <topic> <output_directory>
rosrun pcl_ros bag_to_pcd data.bag /velodyne_points ./pcd