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

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

[Steve Eddins]

What do you mean by "calculate it"? Do you mean calculate its area? Or something else?

[Rik]

Or do you want to draw a polygon like this?

[ADNAN KIRAL]

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.

[ADNAN KIRAL]

In fact, if i can type this equation, it will give the area.

Answer 1

[Ameer Hamza]

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));

[ADNAN KIRAL]

thanks for reply, can I get coordinate vs. total area ?

[Ameer Hamza]

Can you elaborate? Do you want a plot?

[ADNAN KIRAL]

well, in fact. i need to see. lets say.

in 1st coordinate total area=1cm^2

in 2st coordinate total area=2cm^2

in 3st coordinate total area=4cm^2

in 4st coordinate total area=10cm^2

so on...

at the end, i will plot it

can i get that ?

thanks

[Ameer Hamza]

By coordinates do you mean corners of polygon? What is the location of each corner?

[ADNAN KIRAL]

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]

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

[ADNAN KIRAL]

thanks a lot

Answer 2

[Durganshu]

You can use polyarea for accomplishing your task. The documentation is here:

https://in.mathworks.com/help/matlab/ref/polyarea.html

Hope that helps!

[ADNAN KIRAL]

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

Answer 3

[Steven Lord]

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.

[ADNAN KIRAL]

thanks