simple_flow

Computes the dense optical flow with the SimpleFlow algorithm (cv::optflow::calcOpticalFlowSF()).

opencv_apps	1.11 and later (ROS 1), 3.0.0 and later (ROS 2)
ROS	noetic, ROS One, jazzy, kilted, lyrical and later
OpenCV	the optflow module of opencv_contrib
Group	Optical flow and motion, the nodes of which publish `~/flows` (FlowArrayStamped), `~/shift` (Point2DStamped) of phase_corr

Usage

# ROS 2
ros2 launch opencv_apps simple_flow.launch.xml image:=/camera/image_raw debug_view:=false
# ROS 1
roslaunch opencv_apps simple_flow.launch image:=/camera/image_raw debug_view:=false

Try it with the demo video

Download the input video of the demo above, publish it as image with image_publisher, and run the node on it, in the terminals:

wget https://ros-perception.github.io/opencv_apps/media/clips/keybridge.mp4
# terminal 1: publish the video as image in a loop
ros2 run image_publisher image_publisher_node keybridge.mp4 --ros-args -p publish_rate:=10.0 -r image_raw:=image
# terminal 2: run the node with the parameters of the demo
ros2 launch opencv_apps simple_flow.launch.xml image:=image scale:=8 use_camera_info:=false
# terminal 3: view the result
ros2 run rqt_image_view rqt_image_view /simple_flow/image

In ROS 1:

# terminal 1
rosrun image_publisher image_publisher keybridge.mp4 _publish_rate:=10 __name:=camera
# terminal 2
roslaunch opencv_apps simple_flow.launch image:=camera/image_raw scale:=8 use_camera_info:=false

See Credits of the demo videos for the license of the video.

Subscribed topics

Topic	Type
`image`	`sensor_msgs/msg/Image`

Published topics

Topic	Type
`~/flows`	opencv_apps/msg/FlowArrayStamped
`~/image`	`sensor_msgs/msg/Image`

Parameters

Source

src/nodelet/simple_flow_nodelet.cpp, launch/simple_flow.launch.xml

Name	Type	Default (range)	Changed at run time	Description
`queue_size`	int	3	no, restart the node	Specigy queue_size of input image subscribers
`scale`	int	4 (1 - 24)	yes	Scale