how to make arrows

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George
George 2011-5-17
hi there! here is my question. I am using text command to place some text to specific points [x1,y1]=ginput(1); text(x1,y1,'P'); Now, is it possible to draw an arrow from that point (named P) down to x1 ? Can you please tell me how to do that ? Thanks. PS i don't want to make it manually, it has to be done automatically.

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Arnaud Miege
Arnaud Miege 2011-5-18
You can use the annotation function as suggested by Matt. As pointed out, the coordinates need to be normalized. There's a nice utility function on the FEX that does that:
http://www.mathworks.co.uk/matlabcentral/fileexchange/10656-data-space-to-figure-units-conversion
HTH,
Arnaud

更多回答（2 个）

Matt Fig
Matt Fig 2011-5-17
As an alternative, here is a way to do it using the ANNOTATION function. Run the code and click where you would like the text to appear (somewhere in the upper middle), then click again near the parabola.
figure('units','norm')
x = -2:.1:2;
axes('units','norm')
plot(x,x.^2); % Plot a parabola
% The first point will have text, second the arrowhead...
[x1,y1] = ginput(2); % Get two points from user.
A = annotation('textarrow','units','norm','string','Parabola');
% Next we need to transform the GINPUT values to figure units.
XL = get(gca,{'xlim','ylim','pos'});
[XL,YL,P] = deal(XL{:});
Ax = P(3)*(x1-XL(1))/diff(XL)+P(1);
Ay = P(4)*(y1-YL(1))/diff(YL)+P(2);
set(A,'x',Ax,'y',Ay) % Set the arrow in the correct position.
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Matt Fig
Matt Fig 2011-5-17
Good idea Sean de, I will try to get it done in the next day or two.
@Kelly: Right on, I'll look for yours too!
George
George 2011-5-18
Thanks for your reply. But, i have to deal with seismic waves, and zoom in is more than necessery. If you try to zoom in with your script, the function zooms in but the arrow stays where it was before .. i kinda want the arrow to be in the exact same position no matter what.. like if you od it manually and pin it to axes :( i want that but with some code and not manually. Is that possible ? Thanks.

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Sean de Wolski
Sean de Wolski 2011-5-17
doc quiver

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