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Property node to get value (not position) at intensity graph position

Consider an intensity graph with one cursor.

The cursor palette allows one to see the X, Y cursor position/location and value at that position of the cursor.

One can also use a property node to obtain the cursor location.

But I see no property node to obtain the value.  Since LabVIEW must do some interpolations between array positions to get the value seen in the cursor palette, it is not as simple as trying to index the 2d array (for the image in the intensity graph), to get the value.

I would like access to the exact value seen in the dursor palette.  Any comments?

Sincerely,

Don
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Message 1 of 7
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I would like to have a crack at it so is it practical to post an example?

thanks

David

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Message 2 of 7
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Yes, take a look at this.  You will notice that the value shown in the cursor palette rarely matches with the indicator labeled 'value'. Transposing the intensity graph does not result in any better results either...........Don
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Message 3 of 7
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It seems you get only good Z values if you create a cursor that is "locked to plot".
For simplicty, I use a much smaller window (10x20) (Which is also not square so we can see if me accidentally confuse x and y ;)).
 
red cursor: your old free cursor
yellow cursor: cursor is locked to the plot.
 
 
The Z values of a free cursor seem somewhat arbitrary at best. 😉
It does not interpolate, because the values jump at the index boundaries. I tried a few interpolations (bilinear, bicubic, etc.) and nothing seems to correlate consistently with the Z values displayed in the cursor window.
 
Maybe sombody from NI can shine some light on this.
 
Attached is my tester (LabVIEW 8.20).
Message 4 of 7
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Well it looks like you meant 'Snap to Point' and 'Allow Dragging' are the magic combination and indeed that works.

The 'lock to plot' option does not appear to allow a drag even with 'Allow Dragging' set to True (in fact it seems as if the cursor goes away).

Thanks for taking a look.  I can live with the above combination because it allows me to index the 2d array and validate the value seen in the cursor palette.

 

Sincerely,

 

Don

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Message 5 of 7
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Sorry about the lingo confusion. 😉
 
If you think about it, it is not really obvious how a "free" cursor should behave on an intensity graph. By analogy, if you have a free cursor on a waveform graph and move it in the x direction, the y value will no track any graph data. So why should anything happen to the cursor Z on an intensity graph if you move it in x or y unless it is snapped to a plot?
 
The confusing issue here is that the free intensity graph cursor Z value seem to "partially track" the intensity values. They raise and drop with the data to some extent, just not very accurately.
Message 6 of 7
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The other confusing issue is that for the cursor free drag situation on an intensity graph, the cursor is always ON the intensity graph.  There is no visual cue as there is for the cursor free drag situation on the waveform graph where when one drags the cursor off the plot, it is logical that a nonsensical value may appear.....Don
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Message 7 of 7
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