How to convert Python script to ROS script? (Measuring distance between two points using RealSense depth camera)

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You need to follow this steps,

1. Create a ROS node
2. Create a subscriber to receive the depth image data
3. Extract the depth values of the two points from the depth image data
4. Calculate the distance between the two points using the extracted depth values
5. Publish the calculated distance to a ROS topic

Or else, you can also use realsense-ros package to achieve the results. You can calculate the distance of two specific points by this answer #q372672, then subscribe to the camera of real sense and follow others' steps.

#!/usr/bin/env python

import rospy
import cv_bridge
import numpy as np
import pyrealsense2 as rs
from sensor_msgs.msg import Image
from cv_bridge import CvBridge

class distance_measure:
    def __init__(self):
        self.pipeline = rs.pipeline()
        self.pipeline.start(rs.config())
        self.bridge = CvBridge()
        self.sub = rospy.Subscriber('/camera/depth/image_raw', Image, self.depth_callback)
        self.pub = rospy.Publisher('/distance', Float32, queue_size=5)

    def depth_callback(self, data):
        cv_image = self.bridge.imgmsg_to_cv2(data, desired_encoding="passthrough")
        self.depth_frame = cv2.convertScaleAbs(cv_image, alpha=0.01)

        self.color_intrin = rs.video_stream_profile(self.pipeline.get_active_profile().get_stream(rs.stream.color)).get_intrinsics()

        self.x1 = 480
        self.y1 = 550
        self.x2 = 810
        self.y2 = self.y1
        ans = self.calculate_distance()
        self.pub.publish(ans)

    def calculate_distance(self):
        udist = self.depth_frame[self.y1, self.x1]
        vdist = self.depth_frame[self.y2, self.x2]

        point1 = rs.rs2_deproject_pixel_to_point(self.color_intrin, [self.x1, self.y1], udist)
        point2 = rs.rs2_deproject_pixel_to_point(self.color_intrin, [self.x2, self.y2], vdist)

        dist = math.sqrt(math.pow(point1[0] - point2[0], 2) + math.pow(point1[1] - point2[1], 2) + math.pow(point1[2] - point2[2], 2))
        return dist

if __name__ == '__main__':
    rospy.init_node('distance_measure')
    distance_measure()
    rospy.spin()