topic Re: Sliding window over wavetrain in waveform graph? in LabVIEW

Sliding window over wavetrain in waveform graph?

DonRoth — Sat, 12 Aug 2006 19:39:31 GMT

At NIWeek 2006, Michael Cerna gave a very nice presentation in the area of Math & Signal Processing. One of his example VIs I believe was entitled 'Cursor-based Measurement.vi' and in it he showed an interesting method of sliding a window over the signal to compute local properties over just that portion of the waveform that the window covered. The windowed waveform was hilighted in a different color than the remainder of the waveform. I have done something similar with a set of slide controls that allows the length and position of the window to be changed by moving the slides. I am trying to find his example both in the LabVIEW 7.1 and LabVIEW 8 examples and cannot locate it. I want to see how he did what he did and perhaps modify it so that one can lengthen the window by clicking and dragging rather than inputting a length into a numeric control. If this example was written in LabVIEW 8.2, I wonder if could possibly be saved to 8.0 and posted here.

Thanks,

Don

Re: Sliding window over wavetrain in waveform graph?

CoastalMaineBird — Sun, 13 Aug 2006 13:30:55 GMT

I don't know anything about the specific example you cite, but I have been working on the same issue.

I have attached a VI to select a portion of a wave.

Drag either cursor and it drags the "window", but keeps the duration constant.

Hold down SHIFT, and it drags only the one side, changing the duration.

Unfortunately, it's Windows only, because it uses the INPUT DEVICES functions.

If you do it with normal key-down events, it will miss a key-down or key-up even WHILE you're dragging the mouse.

Re: Sliding window over wavetrain in waveform graph?

DonRoth — Mon, 14 Aug 2006 17:52:29 GMT

See the attached. Likely similar to Michael's but he implemented somehow without a slide control. Test this and see what you think. It does not require the keyboard utilities and might be a good cross-platform solution (until I figure out what he did or someone posts it).

Sincerely,

Don

Re: Sliding window over wavetrain in waveform graph?

CoastalMaineBird — Mon, 14 Aug 2006 18:17:44 GMT

Well, you had asked about a "cursor-based" selection method so I gave you that. I have a PICTURE-based one, but it uses a slide control like yours.

If you move the START past the END, your program gets confused. I suspect it's the control itself which is confused.

Anyway, thanks for more ideas.

Re: Sliding window over wavetrain in waveform graph?

DonRoth — Mon, 14 Aug 2006 18:44:20 GMT

Right, the slider method is a little clunky (I'm not crazy about my method which is why I posted in the first place); probably there is a way to make sure end limit (slide) cannot go lower than start limit (slide). I will look at adding that code and re-posting. I think eventually Mike's VI will make its way to this discussion as well. In his method he showed at NI week, there was no cursor visible but I assume somehow he was doing it with cursors. The only thing you saw was the overlay window and he would mouse on that and move the window.

Don

Re: Sliding window over wavetrain in waveform graph?

CoastalMaineBird — Mon, 14 Aug 2006 18:57:21 GMT

The only thing you saw was the overlay window and he would mouse on that and move the window.

Could you stretch and shrink it too?

I suppose you could do it by brute force, detecting clicks on a decoration or something on top of the graph, and moving / stretching / shrinking the decoration when the mouse moves. That's a lot of work, and you'd have to do a lot of coordinate transformation to get real data-coordinates out of it.

Re: Sliding window over wavetrain in waveform graph?

CoastalMaineBird — Mon, 14 Aug 2006 19:02:19 GMT

IN case anybody wants it, here's a way to use a picture to display the data and the sliding, adjustable window.

It uses a MODIFIED copy of the standard PLOT WAVEFORM vi, modified only to bring out the SCALE FACTORS so I can use them later.

It's not very pretty.

Re: Sliding window over wavetrain in waveform graph?

DonRoth — Mon, 14 Aug 2006 19:16:55 GMT

You hit a key point. No, he manually set the window width with a numeric control. I wanted to see if I could modify it so you could stretch it in either direction using some LabVIEW technology. I'm still working v7.1, I'll be upgrading to v8.2 soon and there may have been a technology that he used that was native to v8.2 that I/we don't know about that accomplished things in a less complicated way than we think. Another reason we want to see it. I know in v8 and above, there are cursor-based events that are not available in v7.1.

Don

Re: Sliding window over wavetrain in waveform graph?

DonRoth — Mon, 14 Aug 2006 19:34:03 GMT

This version does some limit checking on the sliders so the end slider cannot be less than the start slider. It also now uses a 'value change' event rather than 'mouse up' event so that the overlay on the graph now slides while moving, shortening, or expanding. It may be in its optimized state right now so at this point, probably time to wait for Michael to post.

Don

Re: Sliding window over wavetrain in waveform graph?

DonRoth — Mon, 14 Aug 2006 19:50:43 GMT

ps. I expect that with cursor-based value change events in v8.0 and above, we can implement a hybrid interface to what you and I have done, but without the keyboard utilities. It would require a 3rd cursor, probably centered between the start and end cursors, that would be used to slide the whole window. When I install v8.2, I can try this as well.....Don

Re: Sliding window over wavetrain in waveform graph?

DonRoth — Mon, 14 Aug 2006 19:59:34 GMT

One of the things I like with your picture control example is the ability to draw a semi-transparent object so that underlay information can be seen. I have always wondered if something like that can be done with the conventional graph containers....Don

Re: Sliding window over wavetrain in waveform graph?

CoastalMaineBird — Mon, 14 Aug 2006 20:17:56 GMT

I have 8.2 beta, but I see nothing in the graph pertinent to making it automatic (a la the demo you saw).

It does have cursor grab/move events (like 8.0).

Your idea of the third cursor in the middle would remove the need for my keyboard, as you could grab either side and stretch/shrink it, or grab the middle and move it.

However, it might be difficult to accurately select small portions. Perhaps the cursor readouut would assist that.

Your scheme also uses an X-Y graph, so it can color the selected portion separately. Since I have 12,000+ points on a graph, I wonder about the re-plotting every time the mouse moves...

Re: Sliding window over wavetrain in waveform graph?

CoastalMaineBird — Mon, 14 Aug 2006 20:22:32 GMT

the ability to draw a semi-transparent object so that underlay information can be seen.

Yeah, it's the GRAYED-OUT RECTANGLE function which does that. Without that, you have a large rectangle blocking your view.

Re: Sliding window over wavetrain in waveform graph?

DonRoth — Mon, 14 Aug 2006 20:52:29 GMT

Does v8.2 only have the cursor grab and move events or are there cursor value change events also? (or maybe the cursor move event simulates a cursor value change event?).....Don

Re: Sliding window over wavetrain in waveform graph?

CoastalMaineBird — Mon, 14 Aug 2006 20:57:27 GMT

The cursor-related events are the same as 8.0

Re: Sliding window over wavetrain in waveform graph?

DonRoth — Mon, 14 Aug 2006 21:00:51 GMT

I implemented my example with an XY graph so I could define the sliding window overlay. If you don't need that, you could probably even use a straight waveform graph. There may even be a creative way to define the sliding window overlay with a waveform graph but my initial thought was to use the XY graph.

With as many points as you have, 12K, have you considered min-max decimation on your data? Damien Gray wrote an article on 'Memory Management in LabVIEW.' I'm sure it can be downloaded from somewhere on ni.com. One of the topics he discusses is min-max decimation and it could be applicable to your situation, depending on the size of your graphs. This method allows faster data display.

.....Don

Re: Sliding window over wavetrain in waveform graph?

DonRoth — Wed, 16 Aug 2006 17:13:56 GMT

I did a few more things as time permitted. I installed LabVIEW 8 and used the 'new' Cursor Move Event to develop the sliding window with 3 cursors as we mentioned earlier. Then I eliminated one of the cursors and used your 'SHIFT' key strategy.

If I can get the cursor to work as shown here AND underly the plot (as simulated in LabVIEW 7.1 by locking cursor to plot and choosing 'None' for cursor point style), we can do something really cool and simulate the picture control draw grayed rectangle by adding cursors between the start and end cursors. I'm not sure how to get this to work right in LabVIEW 8. See thread

http://forums.ni.com/ni/board/message?board.id=170&message.id=200985&jump=true

However, I also need to learn about and experiment with the 'new' draw abilities on graphs. That may allow simulating the picture control draw grayed rectangle and eliminate the need to try to do the same thing with additional cursor draws.

Michael Cerna posted his sliding window VI on NI FTP site and I downloaded; I hope to have time to look at them today or tomorrow and will post after that.

Sincerely,

Don

Re: Sliding window over wavetrain in waveform graph?

DonRoth — Wed, 16 Aug 2006 17:15:17 GMT

ps. Here are the VIs I referred to in the last post. These are in LabVIEW 8.

Re: Sliding window over wavetrain in waveform graph?

CoastalMaineBird — Wed, 16 Aug 2006 17:30:21 GMT

Michael Cerna posted his sliding window VI on NI FTP site and I downloaded;

Can you point me to it? That site has a lot of stuff.

Another thought just struck me (that happens sometimes, despite my best defenses :-):

Instead of an X-Y graph as you did, where the 2nd plot was the selected portion in a different color, suppose you made TWO plots on the waveform graph? The first one is all the data, in the normal color. The 2nd plot is only the selected portion, and it's X0 factor is set to the starting point within the whole waveform. The 2nd plot would overlay the first, to change it's color.

Actually, I seem to remember that plot #0 is painted LAST, so you might have to cange the order, but still. That would look exactly like yours, but not have to be converted into X-Y data.

Just a thought.

Message Edited by CoastalMaineBird on 08-16-2006 12:34 PM

Re: Sliding window over wavetrain in waveform graph?

DonRoth — Wed, 16 Aug 2006 17:54:25 GMT

I think what you suggest for the waveform graph would work just as is seen for the XY graphs. When I first was starting the examples, I just happened to playing with the XY graph so I went in that direction.

I looked at Michael's VI today. First, in reply 5 of this thread, I erroneously stated there was no cursor visible. In fact there is a cursor visible and what is moved to move the window. Sorry about that. In general, he uses the same techniques as shown in the posted VIs (and described in your last post) to overlay a second plot (in this case on a waveform graph). Our methods are probably a little more interesting from the standpoint of being able to adjust both window position and length by just using the cursors.

You can get Michael's presentation demos (I4_Cerna_8.0.zip) from:

ftp://ftp.ni.com/outgoing/

The VI I specifically referred to was called Cursor-based measurement.VI and it is in Folder entitled 'Time-varying and audio.'

Sincerely,

Don