How can I create a fine contour from set of points?

Question

ttopal 2018-9-27

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https://ww2.mathworks.cn/matlabcentral/answers/420977-how-can-i-create-a-fine-contour-from-set-of-points

回答： ttopal 2018-9-28

采纳的回答： KSSV

在 MATLAB Online 中打开

Hi,

I am creating different contours using (x,y) coordinate of points.

Say if i want to create a triangle I would use

x1=(0,0)
x2=(8,-4)
x3=(8,4)
x4=(0,0)

giving me this contour:

But, i need more points on this contour, especially near the edges:

which for various contours i calculate manually.

Now I want to automate this, and add those points near the edges with a given length.

Should I write a for loop, calculate the distance between neighboring points, divide by given length, and use to get the additional points and repeat?

Or is there a better way?

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Answer 1

KSSV 2018-9-27

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x1=[0,0] ;
x2=[8,-4] ;
x3=[8,4] ;
x4=[0,0] ; 
P = [x1 ; x2 ; x3 ; x4] ;
plot(P(:,1),P(:,2)) ;
N = 10 ;
t = linspace(0,1,N)' ; 
L = cell(3,1) ;
for i = 1:3   
    L{i} = [P(i,1)+(P(i+1,1)-P(i,1))*t  P(i,2)+(P(i+1,2)-P(i,2))*t] ;
end
L = cell2mat(L) ;
hold on
plot(L(:,1),L(:,2),'.r')

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ttopal 2018-9-28

Thank you for your time, i thought of linspace too, but the issue is, i need this additional points to be close to edges, sometimes i would have to take N=100 and say if i have shape like this:

i would end up with hundreds of points which increases the System size for later steps dramatically. That's why i am trying to give a predefined size and add points only close to the edges.

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Answer 2

ttopal 2018-9-28

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https://ww2.mathworks.cn/matlabcentral/answers/420977-how-can-i-create-a-fine-contour-from-set-of-points#answer_338808

在 MATLAB Online 中打开

Using @KSSV answer this works a treat:

x1=[0,0] ;
x2=[8,-4] ;
x3=[8,4] ;
x4=[0,0] ; 
P = [x1 ; x2 ; x3 ; x4] ; % set of points
plot(P(:,1),P(:,2)) ;
N = size(P,1)-1 % number of lines 
ratio = 0.04 %how close to the edges you need the points to be added
t = [0+ratio;1-ratio]; % find both ends of the line  
L = cell(N,1) ;
for i = 1:N   
    L{i} = [P(i,1)+(P(i+1,1)-P(i,1))*t  P(i,2)+(P(i+1,2)-P(i,2))*t] ;
end
L = cell2mat(L) ;
hold on
plot(L(:,1),L(:,2),'.r')