Ubuntu18.04+ROS melodic, 运行
roslaunch robot_vision usb_cam.launch报错，
ERROR: cannot launch node of type [usb_cam/usb_cam_node]: usb_cam
ROS path [0]=/opt/ros/melodic/share/ros
ROS path [1]=/home/mc/ros/vision/src
ROS path [2]=/opt/ros/melodic/share解决办法：
sudo apt install ros-melodic-uvc-camera
sudo apt install ros-melodic-image-view
sudo apt install ros-melodic-usb-cam
安装完了可以测试一下USB 相机是否正常运行，
roscore
rosrun uvc_camera uvc_camera_node
rosrun image_view image_view image:=/image_raw
正常情况下，此时可以看到你的USB摄像头正常运行，会有弹出窗口显示摄像头内的影像。
然后，就可以正常地
roslaunch robot_vision usb_cam.launch
本文结束
参考资料
ERROR: cannot launch node of type [usb_cam/usb_cam_node]: usb_cam - 代码先锋网
