In this tutorial you can experiment with the cameras in MORSE and extract the images they capture. You’ll also be able to control the movement of the robot, by giving it direct coordinates of its destination.
You need to install YARP and its Python bindings, by following the YARP section in the installation notes.
Before running a simulation using YARP, it is necessary to open a new shell terminal and start the yarpserver3 program:
We’ll use the Builder API to create the scenario and configure the robot. You can find the finished file in $MORSE_ROOT/share/morse/examples/tutorials/tutorial-2-yarp.py.
The file itself will be very similar to the one created in the first tutorial. We will only add the camera, and change the middleware bindings to use YARP.
If you edit the existing file for the previous tutorial, after configuring the robot, you can add the camera like this:
camera = VideoCamera() camera.translate(x=0.2, z=0.9) atrv.append(camera)
That will include a video camera on top of the robot.
We will also change the motion controller, to have a look at a different type of controller. We’ll use the waypoint controller, which takes as input the coordinates of the destination for the robot.
motion = Waypoint() atrv.append(motion)
Next we need to tell MORSE how the components will communicate using middlewares. This is done with these lines:
motion.add_stream('yarp') pose.add_stream('yarp') camera.add_stream('yarp')
You can now launch the simulation by pressing p on the 3Dview of Blender.
When the simulation starts, it will print the names of the YARP ports that have been created for every corresponding component. These port names can be used to connect to the component from an external program or client.
The simplest method to test the reading and writing of data is by using the terminal clients. For example, to read the Pose data of the robot through a port named /morse/atrv/pose/out, you can type the following in a terminal:
$ yarp read /data/in /morse/atrv/pose/out
To enter the destination coordinates for the robot, write them through a port named /morse/atrv/motion/in, using the command:
$ yarp write /data/out /morse/atrv/motion/in
Then type the three destination coordinates, a toleration distance and the movement speed, separated by spaces, and press enter. For example:
5 7 0 0.5 2
Will make the robot move to within 0.5 meters of the coordinates (5.0, 7.0, 0.0), at a speed of 2 m/s.
YARP provides a tool to display the images it receives through a port. This is very convenient to quickly test that you can transmit video from the simulated environment. You first need to launch the viewer application:
$ yarpview /img/read &
This creates a new port called /img/read. Next you need to connect that port with the output port of MORSE dedicated to the camera, which is: /morse/atrv/camera/out The connection is done with this command:
$ yarp connect /morse/atrv/camera/out /img/read
At this moment, you should be able to see the output of the camera mounted on top of the robot. Instruct the robot to move, using the motion controller, and you’ll see the video image being updated.