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Make an asterisk or point move sinusoidally

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SS
SS 2020-8-1
评论： Cris LaPierre 2020-8-1
Hi, I plotted an asterisk on the image mentioned in the code below. I am supposed to get the asterisk to move in a sinusoidal motion directly on the image. However, with my code, I am getting the asterisk on the image seperately and then a plot of a sine wave separately. How do I combine the two?

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回答（1 个）

Cris LaPierre
Cris LaPierre 2020-8-1
Your code is written to create 2 separate figures. The figure command explicitly tells MATLAB to create a new figure window rather than plotting into the current axes.
In order to combine your two figures onto the same axes, you will need to use the command hold on. Once completed, turn hold off.
Consider this example using an image included with MATLAB.
img = imread('peppers.png')
imshow(img)
hold on
h=plot(100,300,'w*');
hold off
Then, if I wanted to move the asterisk up and down, just change the YData property using the line object variable h:
h.YData = 100;
If I wanted to make it move sinusoidally, I could update the XData and YData properties inside a for loop. You might need to add a short pause in the loop so you can actually see the motion.
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SS
SS 2020-8-1
I did what you suggested and it all worked! However because the image and the plot are overlayed, there is some strange flickering going on when I run it. Do I use a double buffer for this issue
Cris LaPierre
Cris LaPierre 2020-8-1
Not sure. I just tried it on my computer and it didn't flicker at all. If could be due to your graphics card, or it might be related to the size of your image. You might see if some suggestions in this post are helpful.

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