contour_moments

Finds the contours and computes their moments (cv::moments()): the area, the length and the center of mass of each contour.

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
demo of contour_moments

Usage

# ROS 2
ros2 launch opencv_apps contour_moments.launch.xml image:=/camera/image_raw debug_view:=false
# ROS 1
roslaunch opencv_apps contour_moments.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/pool_zoom.mp4
# terminal 1: publish the video as image in a loop
ros2 run image_publisher image_publisher_node pool_zoom.mp4 --ros-args -p publish_rate:=10.0 -r image_raw:=image
# terminal 2: run the node
ros2 launch opencv_apps contour_moments.launch.xml image:=image
# terminal 3: view the result
ros2 run rqt_image_view rqt_image_view /contour_moments/image

In ROS 1:

# terminal 1
rosrun image_publisher image_publisher pool_zoom.mp4 _publish_rate:=10 __name:=camera
# terminal 2
roslaunch opencv_apps contour_moments.launch image:=camera/image_raw

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

Note

~/contours (recommended)

opencv_apps/msg/ContourArrayStamped

Recommended, opencv_apps 3.0.1 and later. The contours, in the order of ~/moments (by the area).

~/image

sensor_msgs/msg/Image

~/moments

opencv_apps/msg/MomentArrayStamped

Parameters

See also the common parameters.

Name

Type

Default (range)

Changed at run time

Description

canny_low_threshold

int

100 (1 - 255)

yes

Canny Edge low Threshold

queue_size

int

3

no, restart the node

Specigy queue_size of input image subscribers

Source

src/nodelet/contour_moments_nodelet.cpp, launch/contour_moments.launch.xml