I have 2 sets of noisy data when plotted against each other forms a parallelogram . I want to simplify this to a simple parallelogram with 4 vertices and find the area within.

[T1, UAPP] = textread('Uapp.txt', '%f %f'); %load data into arrays
[T2, UC] = textread('uc.txt', '%f %f');

Error using textread
File not found.

C = 22*10.^-9;
F = 35*1000;
Q = C.*UC; % calculate Q

subplot(2,2,1); plot(UAPP, Q, 'R-'); title('Lissajous figure'); xlabel('UAPP'); ylabel('Charge (Q)');

max_UAPP = max(UAPP); %*efforts to find verticies*
max_Q = max(Q);

min_UAPP = min(UAPP);
min_Q = min(Q);

avg_UAPP = mean(UAPP);
avg_Q = mean(Q);

D = sqrt(((max_UAPP-avg_UAPP)^2)+((max_Q-avg_Q)^2));

pgon = polyshape([-8 -5 8 5], [-1 1 1 -1]);
subplot(2,2,2); plot(pgon);

POWER = S*F; %calculate power

I don't care much about plotting the parallelogram its just to help me visualise i tried to plot (pgon) with actual values from the graph but had many issues presumably because how small the values were, the current plot is a random unrelated test plot of a parralelogram. all i want to do is calulate the power, which is the area contained in the parralelogram by the frequency F. this should equal approximately 60 watts, any help is much appriciated, ive been stuck on this for over a week looking at different answers and trying various method before finally giving in and posting a question on it. Thank you.

Answer 1

[Star Strider]

It is first necessary to define the boundary and then use polyarea —

T1 = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1188663/Uapp.txt');
T2 = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1188668/Uc.txt');
x = T1{:,2};
y = T2{:,2};

% figure
% plot(x, y)

[k,v] = boundary(x,y,0.5);
ps = polyshape(x(k), y(k));

Warning: Polyshape has duplicate vertices, intersections, or other inconsistencies that may produce inaccurate or unexpected results. Input data has been modified to create a well-defined polyshape.

pwr = polyarea(x(k),y(k))                       % Calculate Power

pwr = 9.9475e+04

[xc,yc] = centroid(ps);

figure
plot(x, y)
hold on
plot(xc, yc, 'p')
plot(x(k), y(k), 'r')
plot(ps)
hold off
grid

Use readtable or readmatrix rather than textread.

.

[tobi]

Thank for the help, I achieved the correct value by using your code and smoothing the data to help with the power calculation. Your the best! Thank you so much!

[Star Strider]

As always, my pleasure!

Answer 2

[KSSV]

smooth the data and use polyarea.