Set value for elements within a polygon

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Anh Mai
Anh Mai 2021-8-7
评论： Anh Mai 2021-8-9
Hi all,
I am new to Matlab and trying to solve a problem with polygon.
I want to create a random 2-D matrix, let's say 100 by 100 as a domain.
domain=ones(100);
Then by enter the x & y coordinates of the polygon, I would like to draw that polygon and set all the elements inside the polygon to a different value.
xv=[40;50;60;50;40];
yv=[60;50;60;70;60];
plot(xv,yv) %plot the polygon
in=inpolygoon(xq,yq,xv,xv);
domain(in)=2;
I am stuck right here, I dont know how to define xq and yq to complete the inpolygon syntax. Please help :(.
Thank you all.

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采纳的回答

Matt J
Matt J 2021-8-7
编辑：Matt J 2021-8-7
Ran in:
If you have the Image Processing Toolbox,
domain=ones(100);
xv=[40;50;60;50;40];
yv=[60;50;60;70;60];
in = roipoly(domain,xv,yv);
domain( in )=2;
imshow(domain); caxis([0,2])
  3 个评论
显示 1更早的评论
Matt J
Matt J 2021-8-8
编辑：Matt J 2021-8-8
That will be very slow. Sean's answer does essentially the same thing, but much faster. My answer will be even faster than that, if you have the required toolbox.
Anh Mai
Anh Mai 2021-8-9
Yup, that's true. That's why I said it might look amateur :)). Thanks again for the solution.

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更多回答（1 个）

Sean de Wolski
Sean de Wolski 2021-8-7
Ran in:
Something along this line will work too. Note, you may need to deal with x/y v. row/col indexing (swap meshgrid for ndgrid).
domain = ones(100);
[xx,yy] = meshgrid(1:100);
xv=[40;50;60;50;40];
yv=[60;50;60;70;60];
% plot(xv,yv) %plot the polygon
xvec = xx(:);
yvec = yy(:);
in=inpolygon(xx(:),yy(:),xv,yv);
domain(sub2ind([100 100],xvec(in),yvec(in)))=2;
imshow(domain); caxis([0,2])
  1 个评论
Matt J
Matt J 2021-8-8
编辑：Matt J 2021-8-8
No need for sub2ind that I can see:
domain( inpolygon(xx(:),yy(:),xv,yv) )=2;

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