XY-graph rendering slows down, especially in PDAs

[Wirer]

It is commonly known that Waveform and XY graphs redraw all their data every time the graph is run (for example in a loop).

I have an application that registers two real-time signals and needs to display the signal in a XY-graph (let's say 10 times per second) so that the whole signals (since the start of the acquisition) is displayed continously. This is very possible in desktop Windows, but in PocketPC PDA too far from it:

Due to "draw-all-again" feature of LV graphs, updating of the graphs gets slower and slower during the execution. Even if the amount of data is quite small, the redraw time gets too long after a short period of acquisition.

"Smooth Updates" should render the image at a separate buffer and dis
play the image when it is ready. However, this feature does not seem to work for PDAs. Is it true?

My opinion is that PDAXYGraph_2x.ctl and PDAWaveformGraph_2x.ctl are not generally usable in PocketPC applications if you need to display real-time data in a loop. They should definitely have an option to change the rendering to achieve a better performance.

Since I have been testing different approaches I haven't found any satisfying solutions yet. One might be creating an own custom graph made with C++, which updates only its new contents. This graph would be called (using call library function) from the PDA VI during data acquisition. It this realistic, has anybody made custom graphs to use with LV?

In generally, is it possible to call external code which will display its own user interface (in PDAs)?

thanks,

Wirer

[Russell_G.]

Sorry for the delay in responding to your questions.

I suspect that �Smooth Updates� is not supported by the LabVIEW PDA Module. To minimize the size of the LabVIEW application for the PDA, the module uses controls and indicators that are native to the PDA OS.

The slow behavior of your application is probably due to the significantly slower CPU speed on a PDA. Please see Chapter 5 of the user�s manual for performance considerations.

For information on calling external code, please see the examples that ship with the LabVIEW PDA module, or check out this link for
information on how to do that.

Russell G.
Applications Engineer
National Instruments

[Wirer]

Thank you for your response.

It is very clear that PDA processors (although we have the fastest one 400MHz and 128MB memory) have low performance compared to the desktop processors. We have seen from other applications that PDAs are quite capable of rendering fast graphics and it should not be the bottleneck for applications. However, it seems that LV PDA graphs are not optimized for displaying real-time data due to the fact that thay are redrawing all the data every time (which is unneeded in some cases). I have taken into account the performance considerations but it does not change the fact that graph rendering is not efficient.

Is there any information that somebody has made a custom graphs for LV?

thanks,

Wirer