Created the edge_detection file for the example 7 tutorial for ROS2

stretch_ros_tutorials/edge_detection.py

@@ -0,0 +1,54 @@
+#!/usr/bin/env python3
+
+import rclpy
+from rclpy.node import Node
+import cv2
+
+from sensor_msgs.msg import Image
+from cv_bridge import CvBridge, CvBridgeError
+
+class EdgeDetection(Node):
+    """
+    A class that converts a subscribed ROS image to a OpenCV image and saves
+    the captured image to a predefined directory.
+    """
+    def __init__(self):
+        """
+        A function that initializes a CvBridge class, subscriber, and other
+        parameter values.
+        :param self: The self reference.
+        """
+        super().__init__('stretch_edge_detection')
+        self.bridge = CvBridge()
+        self.sub = self.create_subscription(Image, '/camera/color/image_raw', self.callback, 1)
+        self.pub = self.create_publisher(Image, '/image_edge_detection', 1)
+        self.save_path = '/home/hello-robot/catkin_ws/src/stretch_tutorials/stored_data'
+        self.lower_thres = 100
+        self.upper_thres = 200
+        self.get_logger().info("Publishing the CV2 Image. Use RViz to visualize.")
+
+    def callback(self, msg):
+        """
+        A callback function that converts the ROS image to a CV2 image and goes
+        through the Canny Edge filter in OpenCV for edge detection. Then publishes
+        that filtered image to be visualized in RViz.
+        :param self: The self reference.
+        :param msg: The ROS image message type.
+        """
+        try:
+            image = self.bridge.imgmsg_to_cv2(msg, 'bgr8')
+        except CvBridgeError as e:
+            self.get_logger().warn('CV Bridge error: {0}'.format(e))
+
+        image = cv2.Canny(image, self.lower_thres, self.upper_thres)
+        image_msg = self.bridge.cv2_to_imgmsg(image, 'passthrough')
+        image_msg.header = msg.header
+        self.pub.publish(image_msg)
+
+def main(args=None):
+    rclpy.init(args=args)
+    edge_detection = EdgeDetection()
+    rclpy.spin(edge_detection)
+
+if __name__ == '__main__':
+    main()