From: Axel Friedrich <lists@...>
Date: 2013-06-13T03:35:02+09:00
Subject: Re: Replot in ruby gnuplot

Hi Lars,

> I need to plot data in real time, reading a file over and over and
> update a the screen. How to implement reread and replot?

Are you on Windows? Or, which OS?

I do something similar as you want to do (on Windows): I write data
coming from an ADC to Disk (using a c-programm), update line by line
each 1..60 seconds, and I read this file with Ruby and send the data
from Ruby to gnuplot, doing 2d-plots, updating the plot each time Ruby
reads a new data line.

For reading the file I use: file-tail.

For "real-time" plotting with gnuplot I took a lot from here and
transfered it to Ruby:
* http://users.softlab.ece.ntua.gr/~ttsiod/gnuplotStreaming.html
*
http://www.lysium.de/blog/index.php?/archives/234-Plotting-data-with-gnuplot-in-real-time.html
* https://news.ycombinator.com/item?id=3210793

I open a pipe to pgnuplot.exe:

@gp = "path_to_pgnuplot.exe"
...
@pipe = IO.popen(@gp, "w")
sleep 2
@pipe.puts "set xtics\n"
@pipe.puts "set ytics\n"
@pipe.puts "set style data #{ @linestyle }\n"
@pipe.puts "set grid\n"
...
@pipe.puts "plot \"-\" title 'CH1', \"-\" title 'CH2', \"-\" title
'CH3', \"-\" title 'CH4', \"-\" title 'CH5'"
...
@pipe.close


On Windows, I have a timeout problem with gnuplot;

# "Anti-timeout" workaround; put this at the very beginning of your
programm
puts "Starting dummy-instance of wgnuplot"
tmppipe = IO.popen(@gp, "w")
sleep 10
tmppipe.close


Hope it helps,
Axel

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