calculate and fill an area between a line and a curve

Question

Enzo 2022-12-11

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评论： Paul 2022-12-14

Hello everyone,

according to the following graph, I would like to fill and compute the area enclosed by the black line and the curve. I need to fill and compute the whole area, which is well under the zero for the curve)

for the line I have 4 points (x1,y1; x2, y2)

and for the curve I have 25.000 points (it's a LFP signal, close to an EEG).

Thanks for your help!

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Answer 1

Stephan 2022-12-11

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编辑：Stephan 2022-12-11

A similar discussion here: https://de.mathworks.com/matlabcentral/answers/1870667-i-got-the-problem-with-polyshape-please-help-me. Once you have the polyshape object you can use the area function on it to calculate the enclosed area for example.

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Enzo 2022-12-14

hello @Stephan unfortunately I wasn't able to achieve the goal. Could you provide some more tips?

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Answer 2

Paul 2022-12-11

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https://ww2.mathworks.cn/matlabcentral/answers/1875992-calculate-and-fill-an-area-between-a-line-and-a-curve#answer_1125702

编辑：Paul 2022-12-11

在 MATLAB Online 中打开

Hi Enzo,

I think fill is what you might be looking for. Assuming that (x1,y1) and (x2,y2) are points on the blue data curve as suggested by the picture in the Question, then we can do this. If that assumption is incorrect, please provide more info on how the endpoints of the black segment relate to the data.

rng(100);

x = 1:25;

y = randn(1,25);

plot(x,y)

grid

x1 = x(7);y1=y(7);

x2 = x(9);y2=y(9);

hold on

plot([x1 x2],[y1 y2],'k','LineWidth',3)

fill([x(7:9)],[y(7:9)],'r')

polyshape and area to compute the area.

area(polyshape(x(7:9),y(7:9)))
ans = 2.2524

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Enzo 2022-12-14

hello @Paul, It seems to not work for me.

Paul 2022-12-14

Can you post relevant data and code to illustrate the problem that you're having?

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