Commandline Logging of data: the plotting
If you want to plot something under linux from the commandline, gnuplot is almost always a good and safe choice.
So we want to plot the table from the sqlite database into a nice graph. We want todo this in a nice way, so no intermediate files.
If we look at sqlite3 output it looks something like this:
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sqlite3 temperature.sql "select * from temperature where sensor=0" 1345395460||26.75 1345395492||26.6875 1345395523||26.75
So to note:
- Time in seconds since 1-1-1970.
- We want to plot the first and 3rd column
Field separator is
To plot the data first, open gnuplot:
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$ gnuplot G N U P L O T Version 4.4 patchlevel 3 last modified March 2011 System: Linux 3.1.1-29-linaro-lt-omap Copyright (C) 1986-1993, 1998, 2004, 2007-2010 Thomas Williams, Colin Kelley and many others gnuplot home: http://www.gnuplot.info faq, bugs, etc: type "help seeking-assistance" immediate help: type "help" plot window: hit 'h' Terminal type set to 'wxt' gnuplot>
First we want to set the field separator:
set datafile separator "|"
Then we want to set the format of the time column (as you can see this matches what we used for date in the previous post):
set timefmt "%s"
Set the X axes to show time.
set xdata time
Set the printed format to HH:MM:SS
set format x "%H:%M:%S"
Now plot the graph:
plot "< sqlite3 ./temperature.sql 'select * from temperature where sensor=0'" using 1:3 with lines
This will give you a nice plot, but it is not perfect.
- A grid would be nice
- Time is off, for me there was a 2 hour offset, because of timezone.
- The graph is scaled between min temp and max temp, would be nicer between 0 and 50.
- Some nice axes titles
So lets fix them in reverse order:
The axes label:
set xlabel "Time (HH:MM:SS) set ylabel "Temperature (Celcius)"
set yrange [0:50]
The time offset (for me it is 2 hours):
plot "< sqlite3 ./temperature.sql 'select * from temperature where sensor=0'" using ($1+60*60*2):3 with lines title "Room"
set term post eps set output 'temperature.eps' set datafile separator "|" set xdata time set timefmt "%s" set format x "%H:%M:%S" set yrange [0:40] set xlabel "Time (HH:MM:SS) set ylabel "Temperature (Celcius)" set grid plot "< sqlite3 ./temperature.sql 'select * from temperature where sensor=0'" using ($1+3600):3 with lines title "room"