31 March 2008 08:55 -
Since a few weeks I have a nokia n810. Mainly because of the ability to login
via ssh on servers I manage. This allows me leave my laptop at home when using
my
recumbent bike, which saves around 1.5 KG of luggage.
But it also allows me to save my track and speed info by using the built-in GPS module.
Saving the track in gpx format is quite easy using maemo-mapper. But maemo-mapper does
not save the speed information, hence I needed something else. Fortunately
the n810 has gpsd running when the gps is in use and also has perl installed. So
my problem was reduced to making a perl script that talks to gpsd.
The first script I needed was a script to save all the information from the gpsd
daemon. The usage is quite simple. Start maemo-mapper and after that run the
perl script. This creates a simple log file.
After returning from your trip you just kill the perl script and copy the logfile
to your desktop machine. Then you run the
plot script:
speedplot.pl speed.log output.png
And you have a graph of your speed during the ride in png format. The speed is averaged
over all the measurements of the last minute, because the speed of a bike is
to low to get an accurate speed measurement from just one sample. An example png can
be found
here.
Taking the n810 with me is quite easy, I put it in my topbag on the back of
the bike. In the bag it still can get a gps fix and it is protected against rain.
I am still thinking how to mount it on the bike to be able to use it for following
a predefined route.
What is a problem though is that I do not get any good altitude samples.
I have to look into that to see if I can fix that and be able to make a
altitude graph.
