Create impoly starting at specific point

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Erik 2013-12-10

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https://ww2.mathworks.cn/matlabcentral/answers/109276-create-impoly-starting-at-specific-point

编辑： KSSV 2019-4-23

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Hey there!

Is there a way to draw a polygon using impoly that starts at one previously defined point?

I can use impoly to create a polygon object that I create by clicking on an image and retrieve the coordinates like in the following example:

figure, imshow('gantrycrane.png'); h = impoly(gca,'closed',false); wait(h)

I can also pre-define a polygon and only change it interactively using

figure, imshow('gantrycrane.png'); h = impoly(gca,[10 10; 20 10],'closed',false); wait(h)

The problem with example one is that there is no starting point constraint. The problem with example two that it does not allow the extend the polygon by clicking (I know I could add vertices by pressing the 'a' key while the pointer is on the object). I like to draw a polygon like in example one by clicking on an image that starts at a given point like in exmaple two. I guess there must be a way to make the polygon 'active' again (like it is in example one) using its handle. Does anybody know if this is possible?

Thanks a lot! Erik