hough_lines

Detects the lines with the standard or the probabilistic Hough transform (cv::HoughLines(), cv::HoughLinesP()).

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	any version of the distributions
Group	Features and shapes, the nodes of which publish `~/corners` (Point2DArrayStamped), `~/lines` (LineArrayStamped), `~/circles` (CircleArrayStamped) and `~/contours` (ContourArrayStamped, `~/hulls` of convex_hull), by the kind of the features

Usage

# ROS 2
ros2 launch opencv_apps hough_lines.launch.xml image:=/camera/image_raw debug_view:=false
# ROS 1
roslaunch opencv_apps hough_lines.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/street.mp4
# terminal 1: publish the video as image in a loop
ros2 run image_publisher image_publisher_node street.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 hough_lines.launch.xml image:=image hough_type:=1 node_name:=probabilistic_hough_lines threshold:=100
# terminal 3: view the result
ros2 run rqt_image_view rqt_image_view /probabilistic_hough_lines/image

Probabilistic Hough transform.

In ROS 1:

# terminal 1
rosrun image_publisher image_publisher street.mp4 _publish_rate:=10 __name:=camera
# terminal 2
roslaunch opencv_apps hough_lines.launch image:=camera/image_raw hough_type:=1 node_name:=probabilistic_hough_lines threshold:=100

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
`~/image`	`sensor_msgs/msg/Image`
`~/lines`	opencv_apps/msg/LineArrayStamped

Parameters

See also the common parameters.

Name	Type	Default (range)	Changed at run time	Description
`hough_type`	int	0 (0 - 1)	yes	Hough Line Methods, 0: Standard_Hough_Transform, 1: Probabilistic_Hough_Transform
`maxLineGap`	double	10.0 (0 - 100)	yes	The maximum gap between two points to be considered in the same line.
`minLineLength`	double	30.0 (0 - 500)	yes	The minimum number of points that can form a line. Lines with less than this number of points are disregarded.
`queue_size`	int	3	no, restart the node	Specigy queue_size of input image subscribers
`rho`	double	1.0 (1 - 100)	yes	The resolution of the parameter r in pixels. We use 1 pixel.
`theta`	double	1.0 (1 - 90)	yes	The resolution of the parameter theta in degrees.
`threshold`	int	150 (50 - 150)	yes	Hough Line Threshold

Source

src/nodelet/hough_lines_nodelet.cpp, launch/hough_lines.launch.xml