waveform chart display slow!

[graduate student 44]

i'm sampling 40 channels at 32000hz. the data is then streamed to be displayed on a seperate computer. i'm reading data in every half second, so i need to display a 40 by 16000 double array every half second. i'm using a waveform chart with "strip chart" update mode. the chart history length is 320000 points, 10 sec data.
the code is run on a AMD athlon 64bit 2.2GHZ machine, 2G RAM and 256mb video card.


somehow the display runs very slowly. i've done some testing and have finally pinpointed that the bottleneck is at displaying the points on the screen. i can probably do some downsampling before plotting, just want to make sure there is no other solution?

[altenbach]

40 DBL channels with a history of 320000 points updated every 500ms is a lot of data! Your charts has to shuffle ~200MB/s on the average wile only a tiny fraction of ot is actually resolved on the screen.

You definitely should downsample our signals, there is no monitor that can display 16000 pixels horizontally. Does the history really need to be that long?

Have a look at a Similar recent discussion for some other ideas.

[DFGray]

You can get a decent decimation-for-display algorithm by searching for "gigalabview" in the search bar above or the main search bar on the ni.com home page. This should speed up your display quite a bit. The article may also give you some data handling tips that would speed you up even more.

[Ben]

THe other suggestions that youhave been offered are valid.

Ideas to speed up chart.
1) Shut off autioscaling.--> Add a button to do "auto-scale once now".
2) Shut down smooth
3) Try different interpolations setting (steps take a long time)
4) Defer front panel updates, update display, un-defer front panel updates.
5) Use thinner lines.
6) Split you 40 channels onto different charts on different tabs and only update the visable tabs.

THat is all that comes to mind at the moment.

Ben

[graduate student 44]

thanks a lot guys! i decimated so that now i plot one point for every 8 points. all work perfectly now.