[Kst] Real-time data display without files ?

[Barth Netterfield]

On Monday 24 April 2006 19:36, you wrote:
> Hi Barth,
>
> Thanks for the feedback.
>
> On 23 April 2006 at 23:07, Barth Netterfield wrote:
> | On Sunday 23 April 2006 10:20, Dirk Eddelbuettel wrote:
> | > Yes, but how would I get it loaded / started? I saw no command-line or
> | > menu option for it ...  Can you give me a pointer as to where to start
> | > digging?
> |
> | In principle, you could write and install a datasource to do this.
>
> Ok, I get the hint that this is non-obvious in terms of tieing it to the
> existing UI.

You don't need to write any UI.  The data sources are designed to be run-time 
plugable into the existing UI - they are not so hard to write.  The only real 
issue for you, I guess, is memory (forgetting old data at the right time).

But I have allways preferred the separate app approach.

> | > edd at basebud:~> /tmp/kstdemo.sh | kst -x 1 -y 2 -
>
> [...]
>
> | Just keep in mind that all data hitting kst will be cached, eventually
> | filling up virtual memory.  I prefer to explicitly cache to disk with the
> | logger, and re-read from kst:
> |
> | edd at basebud:~> /tmp/kstdemo.sh > tmp.dat &
> | edd at basebud:~> kst -x 1 -y 2 tmp.dat
> |
> | the file system will make sure that you never actually read from disk
> | unless you go back before things are buffered... so the performance is
> | going to be basically indestinguishable (sp).
>
> Nice. I tried this at work today, and it works fine.
>
> New problem and question: can kst 'synchronise' separate sources? If I have
> several data streams in different files coming at similar but not identical
> rates and times, then the x-axes 'drift' apart and the simple equations I
> plotted looked 'jagged'.  Do I have to synchronise this in the logging app
> which writes the files for kst?

Sigh... 'fraid so - this is what we do in our apps.  We haven't figured out a 
general case definition of syncing inside of kst.

> | kst can read a couple of very light weight binary formats designed for
> | this. If you decide to go binary, let us know and we can describe them.
> |
> | Remember, on each update, kst will only be reading the unread data; at a
> | 20 Hz aquisition rate and only a few vectors, this will be no trouble I
> | would guess.  We read dozens of channels at a 100Hz/channel aquisition
> | rate.
>
> Ack.
>
> | what is your data?
>
> Fairly high frequency securities price data as well some related data.

well.. that is new :-)
it sure isn't balloon telescope pointing system data,
or mm-wave detector data...
or thermometry...
or helicopter test data...