6 ROS_MASTER_URI

echo $ROS_MASTER_URI

This shows the web address, IP, and port number.

Now enter the following command

roslaunch openni_launch openni.launch

ROS_MASTER_URL is the address of ros_master process or roscore

In fact, you may change this (In .bashrc file, but I would not do that).

In the video that I learned, the URI was like below

http://10.8.0.1:11311

Sometimes, the above IP part(10.8.0.1) is a hostname that needs to be mapped to an IP.

Mine was like this

http://localhost:11311

What does this mean?

To find out, let's run below code

roslaunch openni_launch openni.launch

If above code does not work, make sure if you did the following:

1. In catkin_ws folder,

catkin_make

2. Make sure if you source the setup.bash file

In catkin_make/devel

source setup.bash

3. If it still does not work, install openni-launch with the below code.

sudo apt-get install ros-melodic-openni-launch

The melodic part should be your version of ROS.

Then repeat step 1 and 2.

Now this code should work.

roslaunch openni_launch openni.launch

But I got message that No devices connected.

So I installed freenect-launch,

sudo apt-get install ros-melodic-freenect-launch

then I repeated step 1 and 2, and typed below command.

roslaunch freenect_launch freenect.launch

but still, the device was not connected.

I will fix this and re-upload about this part later :)

 

To conclude, there should be only one ros_master, and there can be several clients environments.

Again, it is the address of roscore or ros_master process.