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Extracting output data from launch file node

asked 2016-04-29 04:01:08 -0500

hilmi gravatar image

updated 2016-05-03 03:16:18 -0500

Hi, I am using ROS hydro 12.04 LTS. Currently I successfully launching the motion tracking node based on openni and kinect. There is the data shown at the terminal whenever there is a motion in front of the kinect camera. However, when I look at rqt_graph , there is no published topic for that data and I am wondering why.

Can anyone suggest on how to extract those data to matlab or other program? I can share the developed package if u want to try it. Thanks for your concern.

I had tried to write a code publishing to a topic on the "blob-parameter" line below but there is an error where the global name for std_msgs not defined and error in code syntax : #!/usr/bin/env python

-- coding: utf-8 --

import rospy import sys import cv2 import as cv from sensor_msgs.msg import Image, CameraInfo from cv_bridge import CvBridge, CvBridgeError import numpy as np from numpy import * import os.path import time from std_msgs.msg import String

def bg_diff(fn_bg,im_in,th,blur):

im_bg = fn_bg

diff = cv2.absdiff(im_in,im_bg)

mask = diff < th

hight = im_bg.shape[0]
width = im_bg.shape[1]

im_mask = np.zeros((hight,width),np.uint8)


im_mask = cv2.medianBlur(im_mask,blur)

im_edge = cv2.Canny(im_mask,100,200)

return im_bg, im_in, im_mask, im_edge

def nothing(x): pass

class bgsub2(): def __init__(self): self.node_name = "bgsub"

    rospy.init_node(self.node_name) = rospy.get_param("~move_threshold", "60")        


    cv2.namedWindow("Motion Edge")
    cv2.createTrackbar("threshold", "Motion Edge",, 255, nothing)

    self.isStart = True

    self.cv_window_name = self.node_name
    cv.NamedWindow(self.cv_window_name, cv.CV_WINDOW_NORMAL)
    cv.MoveWindow(self.cv_window_name, 25, 75)

    cv.NamedWindow("Depth Image", cv.CV_WINDOW_NORMAL)
    cv.MoveWindow("Depth Image", 25, 350)

    self.bridge = CvBridge()

    self.image_sub = rospy.Subscriber("input_rgb_image", Image, self.image_callback, queue_size=1)

    self.depth_sub = rospy.Subscriber("input_depth_image", Image, self.depth_callback, queue_size=1)        

    rospy.loginfo("Waiting for image topics...")
    rospy.wait_for_message("input_rgb_image", Image)
    rospy.wait_for_message("input_depth_image", Image)      

def image_callback(self, ros_image):

        frame = self.bridge.imgmsg_to_cv2(ros_image, "bgr8")
    except CvBridgeError, e:
        print e

    frame = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)    = cv2.getTrackbarPos("threshold", "Motion Edge")       
    if self.isStart == True:
        self.frame_prev = frame
        self.isStart = False

    im_bg,im_in,im_mask,im_edge = bg_diff(self.frame_prev,frame,,blur=7)       
    img_size = im_edge.shape      
    params = cv2.SimpleBlobDetector_Params()      
    params.filterByArea = True
    params.minArea = 10

Blob-parameter detector

    detector = cv2.SimpleBlobDetector(params)        
    keypoints = detector.detect(im_edge)
    print len(keypoints)
    if len(keypoints) != 0:
        for key in keypoints:
        pt= ( int(ptx/ len(keypoints)), int(pty/ len(keypoints)))

        print pt = rospy.Publisher('pointer', std_msgs.msg.String, queue_size=1)


    im_edge = cv2.drawKeypoints(im_edge, keypoints, np.array([]), (0,0,255), cv2.DRAW_MATCHES_FLAGS_DRAW_RICH_KEYPOINTS)

    cv2.imshow("Motion Edge",im_edge)

    self.frame_prev = frame

    self.keystroke = cv2.waitKey(5)
    if self.keystroke != -1:
        cc = chr(self.keystroke & 255).lower()
        if cc == 'q':

            rospy.signal_shutdown("User hit q ...
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1 Answer

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answered 2016-04-29 09:41:41 -0500

Airuno2L gravatar image

You'll need to create a node that subscribes to the topic you're interested in. Once you're node has that data, you can do anything you like with it. If you haven't yet, I'd recommend going through the beginners tutorials.

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i had some problems on publishing the topic itself. Once I can publish the topic then it will be no problem for me to create a node that subscribe to a topic. My lack experience in python code make it harder for me to convert output to a topic. Any chance of helping me on the code syntax?

hilmi gravatar image hilmi  ( 2016-05-03 02:42:29 -0500 )edit

I can share the coding on your email for syntax checking. I had tried on my own for the coding but lots of error occur on the output.

hilmi gravatar image hilmi  ( 2016-05-03 02:43:47 -0500 )edit

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Asked: 2016-04-29 04:01:08 -0500

Seen: 165 times

Last updated: May 03 '16