Is there a polar plot with points only and autoscaling?

[Dr_Laine]

Has anyone improved the polar plot VI to allow for point only plotting (i.e.,markers) and/or autoscaling to fit data?

I read over old polar plot posts in this forum, and besides the few variables in the "polar attributes" cluster, there seems to be only low-level manual manipulation as a method to achieve the same functionality as that of the Waveform Chart or XY Graph.

I plan to transform my r-theta into X-Y, then plot on an X-Y Graph with a polar scale background BMP. I have never tried this, but I expect difficulties trying to implement autoscaling. Has anyone any experience with such an approach?

Thank you.

[DOC-doc]

Hi Laine

Why don't you simply plot it on the X-Y plot (R->Y, theta ->X), that is what I usually do.

Cheers.

[Dr_Laine]

Thanks Doc, that's what I started out doing. However, I wanted to produce an actual polar plot (r-theta on circular coordinates rather than X-Y plane), and I found the built-in polar plot function to be limited.

I did some manipulation of the X-Y chart today to make it represent a polar plot. My example plots a reference circle and invisible limit circle for scaling. It also has 45° reference lines that can be turned on and off (but there is a color problem at speed - any help?). Data is transformed from R-T to X-Y using complex transformation.

Anyone let me know if this can be improved.

Thanks,
Laine

[JohnM 64]

There is a good article in the National Instruments Knowledge Base which explains how to reconfigure the polar plot VI to do points instead of lines. To do this, open the block diagram for the Polar Plot VI, then open the block diagram for the Plot Polar Data VI. In this VI, you will need to replace the Draw Multiple Lines.vi with Plot Polar Data.vi. Here is the link to the Knowledge Base article:

How Can I Plot Points Instead of Lines With Polar Plot.vi?

Using the X-Y graph as you have been trying is another good idea. If you do use a background bmp, however, I would not recommend trying to autoscale the data, as the bmp will not scale with the data.

Jo
hn M
National Instruments

[Dr_Laine]

Yes, I abandoned the BMP idea when I actually thought about it.

My solution is attached. This subVI takes an r array, theta array, threshold radius and graph reference, then outputs the data on an XY graph with a threshold circle and optional reference lines every 45°. It also autoscales itself to 110% of the maximum r, or to a user-set value. The graph on the front panel should have scales and gridlines turned off. Now one can manipulate linetypes/points/colors/scaling/etc. as they would on a standard XY graph (because that is what it is). This subVI is also simple, so it is easily customized.

This has worked well in my application. Is there a better way to post it (rather than being hidden in a discussion thread) so others can use/modify
as they need?


Thanks.