ROS Resources: Documentation | Support | Discussion Forum | Index | Service Status | Q&A
Ask Your Question

[Python] How to get distance from PointCloud2

asked 2017-07-26 15:08:45 -0500

sabruri1 gravatar image

updated 2017-09-27 11:03:51 -0500

jayess gravatar image

Hello guys. I follow this question to extract informations (distance) from PointCloud2 with kinect and ros. I need to get distance of [x,y] pixel in real world.

This is my code

When I run it, I get, for variable "int_data", three fields. But I do not know what they are. They seems like a distance, but I am not sure.

[INFO] [WallTime: 1501099449.999255] int_data (0.008157123811542988, 0.006674010306596756, 0.8540000319480896)

Can anyone explain in detail what they are?

Edit: This is the code that is being linked to:

#!/usr/bin/env python
from roslib import message
import rospy
import sensor_msgs.point_cloud2 as pc2
from sensor_msgs.msg import PointCloud2, PointField

def listen():
    rospy.init_node('listen', anonymous=True)
    rospy.Subscriber("/camera/depth/points", PointCloud2, callback_kinect)

def callback_kinect(data) :
    # pick a height
    height =  int (data.height / 2)
    # pick x coords near front and center
    middle_x = int (data.width / 2)
    # examine point
    middle = read_depth (middle_x, height, data)
    # do stuff with middle

def read_depth(width, height, data) :
    # read function
    if (height >= data.height) or (width >= data.width) :
        return -1
    data_out = pc2.read_points(data, field_names=None, skip_nans=False, uvs=[[width, height]])
    int_data = next(data_out)
    rospy.loginfo("int_data " + str(int_data))
    return int_data

if __name__ == '__main__':
    except rospy.ROSInterruptException:
edit retag flag offensive close merge delete


@l4ncelot, @sabruri1 I have faced an issue, i have used the code and insted of depth of camera, i subscribed to /velodyne_points. Now the issue is that when we have uvs=[[width, height]], the output is as follows (x,y,z):

[INFO] [1659697854.053652]: int_data (-11.6488037109375, -3.0516631603240967, -1.9072492122650146)

and when i consider uvs=[ ], the output is as follows:

[INFO] [1659697107.795461]: int_data (5.123467445373535, 1.491416573524475, -1.0372377634048462)

why the values are different? what is the meaning of uvs? what is the difference between uvs=[[width, height]] and uvs=[ ] ???


Delbina gravatar image Delbina  ( 2022-08-05 06:13:41 -0500 )edit

1 Answer

Sort by ยป oldest newest most voted

answered 2017-10-25 07:27:00 -0500

l4ncelot gravatar image

updated 2017-10-25 07:27:47 -0500

it depends on fields member of sensors_msgs/PointCloud2 message described here in read_points function.

With field_name=None option you read all field names as described here. In your case it seems like default configuration which should be classical cartesian coordinate system x, y, z. Have a look here at section 1.3 Common PointCloud2 field names.

edit flag offensive delete link more

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Question Tools



Asked: 2017-07-26 15:08:45 -0500

Seen: 2,341 times

Last updated: Oct 25 '17