zed_nodelet_example

Stereolabs ZED Camera - ROS Nodelet example

zed_nodelet_example is a ROS package to illustrate how to load the ZEDWrapperNodelet with an external nodelet manager and use the intraprocess communication to generate a virtual laser scan thanks to the nodelet depthimage_to_laserscan

Run the program

To launch the wrapper nodelet along with the depthimage_to_laserscan nodelet, open a terminal and launch:

$ roslaunch zed_nodelet_example zed_nodelet_laserscan.launch

Note: Remember to change the parameter camera_model to 0 if you are using a ZED or to 1 if you are using a ZED Mini

Visualization

To visualize the result of the process open Rviz, add a LaserScan visualization and set /zed/scan as topic parameter

Virtual 2D laser scan rendered in Rviz. You can see the projection of the virtual laser scan on the RGB image on the left

Virtual 2D laser scan rendered in Rviz over the 3D depth cloud. You can see the projection of the virtual laser scan on the RGB image on the left

The launch file explained

The launch file executes three main operations:

1. Runs the Nodelet manager
2. Load the ZED nodelet
3. Load the depthimage_to_laserscan nodelet

To run the Nodelet Manager we use the following line instruction:

<node pkg="nodelet" type="nodelet" name="$(arg nodelet_manager_name)" args="manager" output="screen" />

the Nodelet Manager is the process that loads the ZED and the depthimage_to_laserscan nodelets and that allows them to us intra-process communication to pass elaboration data.

The "variable" nodelet_manager_name is defined here:

<arg name="nodelet_manager_name" default="zed_nodelet_manager" />

The ZED nodelet is loaded using its own nodelet launch file:

<include file="$(find zed_wrapper)/launch/zed_camera_nodelet.launch">

called passing the "variable" nodelet_manager_name as parameter:

<arg name="nodelet_manager_name" value="$(arg nodelet_manager_name)" />

The DepthImageToLaserScanNodelet nodelet is loaded with the following commands:

        <node pkg="nodelet" type="nodelet" name="depthimage_to_laserscan" args="load depthimage_to_laserscan/DepthImageToLaserScanNodelet zed_nodelet_manager">
             <param name="scan_height" value="10"/>
             <param name="output_frame_id" value="$(arg left_camera_frame)"/>
             <param name="range_min" value="0.45"/>
             <remap from="image" to="$(arg depth_topic)"/>
        </node>

it is really important to notice these two lines:

<param name="output_frame_id" value="$(arg left_camera_frame)"/>

<remap from="image" to="$(arg depth_topic)"/>

The first line tells to the depthimage_to_laserscan nodelet which is the frame name of the virtual scan message.

The second line tells to the depthimage_to_laserscan nodelet which is the depth image topic to use to extract the information to generate the virtual laser scan.

For the description of the other parameters please refer to the documentation of the depthimage_to_laserscan package