[Gnuplot-info] Plotting multiple columns from stdin

[Bennett, S. \(GE Infrastructure\) <Sil...@ge...>]

Hi All,

I have observed some strange behavior with gnuplot recently. I am =
running Gnuplot version 4.0 patchlevel 0 ( packaged in Debian / Etch ). =
I will demonstrate the problem I am having with a simplified case:

#!/bin/bash

{
	echo 'plot "-" using 1:2 with lines, \'
	echo '"" using 1:3 with lines'
	echo '0 1 2'
	echo '1 2 3'
	echo '2 3 4'
	echo '3 4 5'
	echo '4 5 6'
	echo '5 6 7'
	echo 'e'
} | gnuplot -persist
### End Bash Script

This outputs the following message with no plot:=20

>gnuplot> plot "-" using 1:2 with lines, "" using 1:3 with lines
>                                                                        =
             ^
>	line 7: no data point found in specified file

Is this a feature or a bug?  ;0)

This next script demonstrates that the concept is right in that it =
generates the plot that you would expect.

#!/bin/bash

{
	echo 'plot "-" using 1:2 with lines'
	echo '0 1 2'
	echo '1 2 3'
	echo '2 3 4'
	echo '3 4 5'
	echo '4 5 6'
	echo '5 6 7'
	echo 'e'
} | gnuplot -persist
### End Bash Script


The plot I am asking for in the first script works if I read from a file =
instead of stdin:

### This is the contents of testdata.txt ###
0 1 2
1 2 3
2 3 4
3 4 5
4 5 6
5 6 7
### End of testdata.txt ###

#!/bin/bash
{
	echo 'plot "testdata.txt" using 1:2 with lines, \'
	echo '"" using 1:3 with lines'
} | gnuplot -persist
### End Bash Script

This script generates the appropriate plot.


Looking around on the net to try to find the solution to this problem I =
came across this link:
http://groups.google.com/group/comp.graphics.apps.gnuplot/browse_thread/t=
hread/593fd1647d96eb6b/06b84b965f06e4d7?q=3Dno+data+point+found+in+specif=
ied+file&rnum=3D3#06b84b965f06e4d7

using the concept outlined there, the original script could be written =
as such:

#!/bin/bash

{
	echo 'plot "-" using 1:2 with lines, \'
	echo '"-" using 1:3 with lines'
	echo '0 1 2'
	echo '1 2 3'
	echo '2 3 4'
	echo '3 4 5'
	echo '4 5 6'
	echo '5 6 7'
	echo 'e'
	echo '0 1 2'
	echo '1 2 3'
	echo '2 3 4'
	echo '3 4 5'
	echo '4 5 6'
	echo '5 6 7'
	echo 'e'
} | gnuplot -persist
### End Bash Script

This works, but presents a bigger problem...

Now moving away from the simple case, I need to plot 48 channels of =
floating point data from a 125Hz (as much as 4KHz) streaming source. I =
need to plot about 1000 data points per channel and have the plot =
refresh as quickly as possible.

I could store the data in a buffer and re-echo it to gnuplot 48 times =
but I take a huge performance hit when I do. Similarly I could rewrite =
(overwrite) the data to a file and plot the file, but that kills the =
performance as well.

Any ( Suggestions / Help / Commiserations / RTFM's followed by a link to =
the M ) will be appreciated.

Cheers,
Silas Bennett

=3D0)

Silas L Bennett
GE Security
Scientist / Engineer

T 858 605 5500 x 323
F 858 605 5501
sil...@ge...
www.gesecurity.com

15175 Innovation Dr.
San Diego, CA 92128
USA