Maritime navigation with a Rasp Pi and OpenCPN

Setting up the GPS

After installing Raspbian, it is time to configure the services needed for the DIY navigational device. The GPS daemon gpsd can be used to control the external GPS mouse. It connects directly with the serial interface, which provides access to the system, and allows incoming connections by OpenCPN.

The program acts as a connector between the two components. To set up the program on the computer, you should first install the necessary packages:

$ sudo apt-get install gpsd gpsd-clients python-gps

Then, enter the path for the interface in the DEVICES line of the /etc/default/gpsd file. In this case, the path for the Navilock NL-402U would be /dev/ttyACM0. You should also add a -b in the GPSD_OPTIONS line. Finally, restart with

service gpsd restart

The service now waits for incoming connections. You can tell whether everything is functioning by calling cgps in the command line. After connecting the GPS mouse, you should wait a few minutes to get a GPS fix. The length of the wait will depend on your location.

Setting Up OpenCPN

OpenCPN stands for Open Source Chart Plotter/Navigator. The program is released under GPLv2 and can be downloaded directly from the project homepage [5]. However, Raspbian itself does not offer a package in its repositories for immediate installation. The community has jumped in to offer an updated OpenCPN package in version 4. After downloading [6], you should use the following invocation for installation:

$ sudo dpkg -i opencpn_4.0.0-1_armhf_tides_map.deb

The first attempt at installation of this package will fail because of unfulfilled dependencies, which you can take care of with:

sudo apt-get -f install

Then OpenCPN will be completely installed and theoretically ready to start.

The Raspberry Pi works fast enough for the task at hand. Even so, a few simple tricks allow better use of OpenCPN, including setting the frame buffer depth to 32 and deactivation of the alpha channels in the frame buffer. To put these settings in place, you should edit the /boot/config.txt file, find the following line, and assign the settings shown:

framebuffer_depth=32
framebuffer_ignore_alpha=1

Because these modifications apply to the hardware, it is necessary to reboot before they take effect.

After a reboot, you should start OpenCPN via the corresponding entry in the Raspbian desktop menu. The main configuration dialog will appear when the program is started for the first time (Figure 2).

Figure 2: When configuring OpenCPN, activate the connection to the GPS daemon (GPSD) and enter the path to the waterway maps.

The dialog displays options for various parameters for the boat, connections to the GPSD, and the maps being used. The User Interface entry lets you specify the language for OpenCPN.

The software implements modifications to the language setting after a restart, at which point the configuration dialog will reappear. Once the language is appropriately set, you should click on Connections and then on Add Connection. You should select the GPSD protocol with address 127.0.0.1. One mouse click on Apply activates the modifications.

When finished, you should specify where the maps are located. The "Waterways" box explains sources for suitable maps. You should load these maps onto the Rasp Pi and note their storage location; then, you should go to the configuration menu, click on Add Directory under the Chart Files tab, and select the folder in which the maps have been placed. Now, set a checkmark at Scan Charts and Update Database and click on Apply then OK. Within a few minutes OpenCPN will build an internal data base of maps.