line_segment_detector

Detects the line segments with the line segment detector (LSD, cv::LineSegmentDetector).

opencv_apps	3.0.0 and later
ROS	ROS One, jazzy, kilted, lyrical and later
OpenCV	OpenCV 3.0 - 3.4.5 or 4.5.4 or later, which have cv::createLineSegmentDetector()
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 line_segment_detector.launch.xml image:=/camera/image_raw debug_view:=false
# ROS 1
roslaunch opencv_apps line_segment_detector.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 line_segment_detector.launch.xml image:=image lsd_density_threshold:=0.3 lsd_line_length_threshold:=10.0 lsd_refine_type:=2 lsd_scale:=0.4
# terminal 3: view the result
ros2 run rqt_image_view rqt_image_view /line_segment_detector/image

In ROS 1:

# terminal 1
rosrun image_publisher image_publisher street.mp4 _publish_rate:=10 __name:=camera
# terminal 2
roslaunch opencv_apps line_segment_detector.launch image:=camera/image_raw lsd_density_threshold:=0.3 lsd_line_length_threshold:=10.0 lsd_refine_type:=2 lsd_scale:=0.4

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
`lsd_angle_threshold`	double	22.5 (0.1 - 179)	yes	Gradient angle tolerance in degrees
`lsd_density_threshold`	double	0.7 (0 - 0.9)	yes	Minimal density of aligned region points in the enclosing rectangle
`lsd_line_length_threshold`	double	100.0 (0 - 1000)	yes	Threshold of line length. Shorter lines are not published nor drawn.
`lsd_log_eps`	double	0.0 (0 - 360)	yes	Detection threshold: -log10(NFA) > log_eps. Used only when advanced refinement is chosen
`lsd_n_bins`	int	1024 (1 - 10000)	yes	Number of bins in pseudo-ordering of gradient modulus
`lsd_quant`	double	2.0 (0 - 100)	yes	Bound to the quantization error on the gradient norm
`lsd_refine_type`	int	0 (0 - 2)	yes	Line Segment Detector Modes, 0: REFINE_NONE, 1: REFINE_STD, 2: REFINE_ADV
`lsd_scale`	double	0.8 (0.1 - 1)	yes	The scale of the image that will be used to find the lines. Range [0.1..1]
`lsd_sigma_scale`	double	0.6 (0.1 - 10)	yes	Sigma for Gaussian filter. It is computed as sigma = _sigma_scale/_scale
`queue_size`	int	3	no, restart the node	Specify queue_size of input image subscribers

Source

src/nodelet/line_segment_detector_nodelet.cpp, launch/line_segment_detector.launch.xml