Some questions about velodyne_pointcloud package

asked 2014-08-03 03:10:42 -0500

Lau
45 ●6 ●9 ●13

updated 2014-08-03 04:04:47 -0500

Hello! I am learning ROS recently . I have some questions about velodyne package:

After I run "$roslaunch velodyne_pointcloud 32e_points.launch calibration:=/home/llm/catkin_ws/src/velodyne_pointcloud/params/32db.yaml" in the terminal , which .cpp file in src/conversions/ was executed ?
I notice that in the file convert.cpp , "output_" publish a "outMsg" (velodyne_rawdata::VPointtCloud::Ptr) in line 78,but in line 31 ,the "output_" advertise "sensor_msgs::PointCloud2" message ,I can not understand this code.
I am focused on this one . I created a node to subscribe the topic "velodyne_points" , and I want to extract the information of the points's XYZ coordinate value from the topic , but I can not understand the message type "sensor::PointCloud2", what should I do?

Looking for you reply ! Thank you very much !

answered 2014-08-03 09:34:01 -0500

joq
25443 ●181 ●256 ●408

updated 2014-08-04 09:17:24 -0500

That launch file runs the cloud nodelet in a velodyne_nodelet manager process. The cloud nodelet is built using cloud_nodelet.cc and convert.cc.
The constructor must advertise the topic before the callback can publish to it.
An example of reading the individual points in the message is here in RingColors::convertPoints, a method that reads /velodyne_points and publishes a colored cloud containing the same points in /velodyne_rings.

EDIT: To run the Ring Colors nodelet, you can create your own launch file, something like this (untested):

<include file="$(find velodyne_pointcloud)/launch/32e_points.launch" />
<node pkg="nodelet" type="nodelet" name="ring_colors_nodelet"
      args="load velodyne_pointcloud/RingColorsNodelet velodyne_nodelet_manager" />

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Thank you . 1. For the second question , I mean that the "outMsg" is not a type "sensor_msgs::PointCloud2" message . In my previous study , I noticed that the types should be same like the code(copied from the tutorials) listed : { ros::Publisher chatter_pub = n.advertise<std_msgs::string>("chatter", 1000); ... std_msgs::String msg; ... chatter_pub.publish(msg); } 2. For the third question. If I want to run the ringcolors_nodelet.cc and colors.cc and read the point's message , should I creat a .launch file like the cloud_nodelet.launch and add it to 32e_points.launch?

Lau ( 2014-08-04 02:41:31 -0500 )edit

pcl_ros and pcl_conversions provide a callback interface for the PointCloud2 message, converting it to a PCL point cloud, which the code can conveniently manipulate.

joq ( 2014-08-04 09:08:26 -0500 )edit

Thank you ! now I can read the individual point now !

Lau ( 2014-08-04 18:21:35 -0500 )edit

If this answers your question, please click the check mark.

joq ( 2014-08-05 08:35:21 -0500 )edit

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