get world coordinates from image coordinates

asked 2018-10-11 16:18:07 -0500

ashkan_abd gravatar image

hi everyone, I now maybe someone asked this question before but I can't found my answer in this forum.
I have a calibrated virtual single camera in gazebo8 and ROS kinetic, after applying some opencv filters, now an object was detected in x = 79.0, y = 23.0, w = 28.0, h = 127.0 coordinates of image. and was published this info into /robot0/object topic.
I'm using image_geometry package to get position of that object in gazebo simulated world, also I know position of that object in this case x = 245 , y = 269 ,I'm using gmapping package and size of map has set to 500 , 500.
this is my code that get object info from /robot0/object topic and try to guess object position in gazebo simulated world :

def get_object(array):
    global img_geo,robot_odometry
    u =[0] + ([2] // 2)
    v =[1] +[3]
    time = rospy.Time(0)
    listener = tf.listener.TransformListener()
    camera_point = img_geo.projectPixelTo3dRay((img_geo.rectifyPoint((u, v))))
    point_msg.pose.position.x = camera_point[0] + robot_odometry.pose.pose.position.x
    point_msg.pose.position.y = camera_point[1] + robot_odometry.pose.pose.position.y
    point_msg.pose.position.z = 0
    point_msg.pose.orientation.x = 0
    point_msg.pose.orientation.y = 0
    point_msg.pose.orientation.z = 0
    point_msg.pose.orientation.w = 1
    point_msg.header.frame_id = img_geo.tfFrame()
    point_msg.header.stamp = time
        listener.waitForTransform(img_geo.tfFrame(), 'map', time, rospy.Duration(1))
        tf_point = listener.transformPose('map', point_msg)
        print(convert_from_robot_to_map(tf_point.pose.position.y, tf_point.pose.position.x))
    except Exception:

def convert_from_robot_to_map(robot_y, robot_x):
    global map_info
    map_x = (robot_x - /
    map_y = (robot_y - /
    return map_y, map_x

but unfortunately printed result isn't true. printed info (print(convert_from_robot_to_map(...))) is y = 250 , x = 249 that is almost robot position in map( robot position in this case is x = 250 , y = 250), and camera_point object from projecting pixel to 3d ray in this case is (-0.23228537548412242, 0.0925648488771315, 0.9682330572174006) . and tf_point object values is(-2.3449200226706126, 0.910935376894018).
I also passed my camera info to img_geo.fromCameraInfo().
What is wrong in this code?? what should I do to get true coordinates of object in gazebo world???

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I think you misunderstand something here. When you check the map size, you get (500,500) which means you have 500 cells (or pixel, they are squares which side equals the resolution) on the width and 500 cells on the height. So if resolution is 0.01 (1cm) you map width is 5m and height 5m

Delb gravatar image Delb  ( 2018-10-12 02:23:19 -0500 )edit

So your robot coordinates aren't (245,269) it means that the robot is on the 245th cell on the width and the 269th cell on the height. The true coordinates of your robot is (245*resolution,269*resolution). In your function you think you return map_x/y but in reality you return cells indexes.

Delb gravatar image Delb  ( 2018-10-12 02:26:49 -0500 )edit

hi @Delb thanks for replying, (245 , 269) is my object position in map and I found this coordinates from monitoring gmapping and I know my convert_from_robot_to_map function gaves me passed position cell indexes in gmapping , how can I get theese indexes for object from below code?

ashkan_abd gravatar image ashkan_abd  ( 2018-10-12 09:35:36 -0500 )edit