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how can i calculate a complex polygon with coordinates in matlab ?

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ADNAN KIRAL
ADNAN KIRAL on 19 Oct 2020
Commented: ADNAN KIRAL on 19 Oct 2020
Hi,
how can I calculate A complex polygon in Matlab?
image shows what I need to calculate in Matlab. do you guys have any code for that ? or are there any Matlab command which can calculate it by coordinates?
thanks in advance

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ADNAN KIRAL
ADNAN KIRAL on 19 Oct 2020
thanks for your reply.
calculation of the area !.
I have a large number of coordinates. If I can code it in Matlab. I will replace with my coordinates. So that I need to know how to calculate the area of such shape.

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Accepted Answer

Ameer Hamza
Ameer Hamza on 19 Oct 2020
The equation in your comment can be written in MATLAB like this
A = 1/2*sum(x(1:end-1).*y(2:end)-y(1:end-1).*x(2:end));

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ADNAN KIRAL
ADNAN KIRAL on 19 Oct 2020
well, suppose, you have a number of coordinates.
x=[.....];
y=[.....];
this is total area A = 1/2*sum(x(1:end-1).*y(2:end)-y(1:end-1).*x(2:end));
up to here, it is ok,
assume i have 100 coordinates.
coordinate 1 (first one), total area= 1cm^2
coordinate 2 (second one), total area= 5cm^2
.. so on..
I just want to give a number to each coordinate (like 1,2,3,4,5....). this part will appear in x coordinate, total areas will be in the y-axis. that is all I want.
like this;
thanks!
Ameer Hamza
Ameer Hamza on 19 Oct 2020
You can try something like this
X;
Y;
A = zeros(1, numel(X)-2);
for i = 1:numel(A)
x = X(1:i+2);
y = Y(1:i+2);
A(i) = 1/2*sum(x(1:end-1).*y(2:end)-y(1:end-1).*x(2:end));
end

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More Answers (2)

Deeds
Deeds on 19 Oct 2020
You can use polyarea for accomplishing your task. The documentation is here:
Hope that helps!

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ADNAN KIRAL
ADNAN KIRAL on 19 Oct 2020
thanks for reply.
one more question please ? how can I get coordinate vs. area ( at the end, I need to know how the area is increasing with coordinate change)
I have tried "cumsum" Matlab command, but it did not work. it gave the total area. thanks

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Steven Lord
Steven Lord on 19 Oct 2020
If you want to do more than just compute its area I would use polyshape for that.
>> x = [7 7 5 3 -5 0 -8 2 -4];
>> y = [-7 3 -6 3 3 8 3 -3 -8];
>> P = polyshape(x, y);
>> plot(P)
There are a number of questions you can ask about a polyshape and a number of operations you can perform on one.

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