Draw line on graph

[MSS]

I want to draw a line on graph using mouse and shall be able to drag and drop anywhere in the graph and if two lines are intersects, I want to read XY values of intersection.

How to program it?

[Dennis_Knutson]

Would a simple cursor do? No programming involved.

[Ben]

Occam would proud of you Dennis!

Ben

[MSS]

How cursors can be used?

[Ben]

"How cursors can be used?"

See here.

Ben

[Dennis_Knutson]

Right click on the graph and select Visible Items>Cursor Legend. Right click in the cursor legend and select Create Cursor>Single Plot. The cursor will be locked to the plot and you can drag it whereever you want and the x/y coordinates of the plot will be in the cursor legend.

Ben,

KISS would also be applicable.

[MSS]

with this I can draw only straight lines. I want to draw tangent lines.

[Dennis_Knutson]

Well, you could have mentioned that in the first place.

Offhand, I don't know an easy way to draw random lines and have the ability to drag them around. Will have to think about that for a while.

[Ben]

I'll offer an outine that makes use of cursors just to KISS.

Add four cursors to your graph and label them such that a pair of cursors define a line.

When the cursors move, redraw the lines. (how to draw lines depends on data type of graph but generally this should be a seperate plot for each line).

After re-drawing the lines, do some basic algebra to compute the intersection then update an indicator (or use an anotation) with the new values.

Code as far as you can then post your code along with images of same and someone will give you a push to get you over the hurdle.

Ben

[altenbach]

Just use mouse down events, transform the mouse position to plot coordinates, and then draw whatever you want using the "plot images" overlay feature.

Here's an old example using an intensity graph, but it works with any other graph (xy, waveform) equally well.

http://forums.ni.com/ni/board/message?board.id=170&view=by_date_ascending&message.id=269593#M269593