[Gnuplot-info] Re: Plotting multiple columns from stdin

[Matti P. <ma...@pi...>]

Hans-Bernhard Bröker wrote:

> Bennett, Silas (GE Infrastructure) wrote:
>>> 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?
>
> A feature.  Of your command script as much as of gnuplot
>
> The problem is that you're trying to read the same inline data set
> twice. That's not how inline data work.  You would have to split you
> your multi-column data into separate datasets, with one 'E'nd-of-data
> per file mentioned in the plot:
>
>     plot "-" u 1:2, "" u 1:2
>        1 2
>        4 5
>            E
>        1 3
>        4 6
>        E
>
>> 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.
>
> That's really not the kind of work gnuplot was ever meant for.  It's not
> a real-time plotting engine, but an interactive program with a scripting
> language.   It's not explicitly made slow, neither is there *any* kind
> of real-time guarantee.
>
>> 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.
>
> No need to re-echo all of it --- just echoing the actual columns used
> would be sufficient, i.e. two columns per '' in the command.
>
>
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To create a kind of rolling plot (oscilloscope) I fount a neat trick: 
create a bitmap of the axes, and create a blank bitmap of the data. At 
each point in time that you wish to add a new data point, add a new 
column to one side of the data bitmap while cutting one off from the 
other side, turn on the pixel at the appropriate row for the data, and 
then create the final image by combining the two bitmaps. A windows/MFC 
implementation can be found at 
http://www.codeproject.com/miscctrl/oscope.asp
Matti