### 1. Prerequisites This code will make use of DiscoverCCRI's [RoverAPI](https://github.com/DiscoverCCRI/RoverAPI), which is designed to make operation of DiscoverCCRI's rovers easy. If you are unfamiliar with the Discover project, please check out our [website](https://discoverccri.org) to learn more. The tutorial assumes that you have already set up a development environment based on the [previous tutorial](starting.md).
### 2. The Code For this tutorial, we will write a simple python script that will make use of the rover's movement, camera, and lidar capabilities. We will direct the rover to drive alone a fixed path, take photos at regular intervals, and record laser scan data from the lidar.
#### 2.1 Writing the Code First, access your development environment using the instructions from the [previous tutorial](starting.md), open the terminal and change into the beginner_tutorials directory you created: ``` cd ~/beginner_tutorials ```
Download the python code for this tutorial and make it an executable file: ``` wget https://raw.githubusercontent.com/DiscoverCCRI/RoverAPI/main/examples/first_script.py chmod +x first_script.py ```
You can view and edit this code with `vim first_script.py` or view the code below: ``` #!/usr/bin/env python3 # license removed for concision from rover_api.discover_rover import Rover from rover_api.discover_camera import Camera from rover_api.discover_lidar import Lidar from rover_api.discover_utils import finish_experiment # initialize the objects to control the hardware rover = Rover() lidar = Lidar() cam = Camera() # take a rosbag recording of the lidar data lidar.start_recording() # drive in a 1 meter square for i in range(4): # drive forward at a rate of 0.2 m/s for 5s rover.move_forward(0.2, 5) # save an image of what the rover sees cam.get_jpg() # turn right at a rate of 15 deg/s for 6s rover.turn_right(15, 6) # stop the recording lidar.stop_recording() # finish the experiment - this will automatically call our finished_cb func finish_experiment() ```
#### 2.2 Explanation ``` #!/user/bin/env python3 ``` Every script we write will contain this [shebang](https://en.wikipedia.org/wiki/Shebang_(Unix)), which lets the computer know which type of interpreter to use when running scripts as executables.
``` from rover_api.discover_rover import Rover from rover_api.discover_camera import Camera from rover_api.discover_lidar import Lidar from rover_api.discover_utils import finish_experiment ``` For this experiment, we will need to access the rover's lidar, camera, and movement capabilities. Additionally, we will need to use the finish_experiment() function to let the system know that our experiment is done.
``` # initialize the objects to control the hardware rover = Rover() lidar = Lidar() cam = Camera() ``` First, we will instantiate the objects to actually access and control the rover's hardware.
``` # take a rosbag recording of the lidar data lidar.start_recording() ``` Next, we will start recording the data from the lidar. The data will be saved to a [rosbag](http://wiki.ros.org/rosbag). If you are unfamiliar with [ROS](https://ros.org), that is alright. Nothing in this API requires you to know ROS, and in the future, we will save the lidar data to a more common format.
``` # drive in a 1 meter square for i in range(4): # drive forward at a rate of 0.2 m/s for 5s rover.move_forward(0.2, 5) # save an image of what the rover sees cam.get_jpg() # turn right at a rate of 15 deg/s for 6s rover.turn_right(15, 6) ``` We will tell the rover to drive forward for 5 seconds at a rate of 0.2 meters per second. This will move the rover forward 1 meter. Then we tell the rover to save a .jpg image of what the camera is seeing. These images will automatically be saved to the `/experiment` directory. After taking the photo, the rover will turn right at a rate of 15 degrees for 6 seconds, making a complete 90 degree turn. Finally, we will tell the rover to repeat this series of steps 4 times, driving in a 1 meter by 1 meter square.
``` # stop the recording lidar.stop_recording() ``` Next, we will direct the lidar to stop recording. This will save the rosbag file to the `/experiment` directory.
``` # finish the experiment finish_experiment() ``` Finally, we will tell the system that you are finished running your experiment. This allows the system to shut down the docker container that our code is running in, and saves the `/experiment` container with all of our data.