calculate and fill an area between a line and a curve

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!

Answer 1

[Stephan]

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.

[Enzo]

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

Answer 2

[Paul]

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

[Enzo]

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

[Paul]

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