Generating Forecast Image

Apache FOP was a convenient choice because I can define a template and merge it with a data file, although it glosses over the generation of the template and XML data file. The Bash script parses all weather data and simply creates an XML data file that matches the requirements of the template I have created. With FOP and OpenJDK installed, I generated a PNG file with:

fop -xml <xml input fn> -xsl <xsl template>-png <output fn>

In my weather template, I tried to include as much information as possible. The script examined the weather description and selected a matching graphic, which is friendlier than pure text. Unfortunately, the forecast has a lot of information (Figure 4).

Figure 4: Weather and forecast.

Miscellaneous Configuration

The standard default for the Raspberry Pi is for the screen to blank after a certain amount of inactivity. Inactivity is inevitable when you don't have a keyboard or mouse attached to the picture frame system. To control this behavior, go to the X server configuration file (i.e., /etc/lightdm/lightdm.conf for the Raspberry Pi) and add the line:

xserver-command=X -s 0 -dpms

This setup might already exist in the default section but will need to be uncommented. According to online sources, you will find this line under the [SeatDefaults] section, but in my case, the section was called [Seat:*].

Scheduling

The various scripts that perform the individual tasks are run by the cron daemon (Listing 3). Because only one thing can be displayed on the screen at a time, the crontab entries have been organized in such a way that twice an hour the weather and forecast are retrieved and displayed at times that normal photographs are not.

#
# next image
0,10,15,20,25,30,40,45,50,55 * * * * /home/pi/screensaver/showpic.sh > /dev/null 2>&1
#
# get and show current weather
4,34 * * * * /home/pi/screensaver/getweather.sh > /dev/null 2>&1
#
# simply copy everything from Dropbox each week
1 1 1,7,14,21,28 * * /home/pi/screensaver/forcesync.sh > /dev/null 2>&1