How to extract data from fnplt plot?

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Lu Da Silva
Lu Da Silva 2021-4-10
回答： Abhaya 2025-1-20
I created two plots using the fnplt function. One plot represents the chord length (c) over the radial position, the other the thickness (t) over the radial position (-> they both have the same x-axis).
The chord and thickness values are calculated via ppmak function (with breaks and coefficients):
chord = ppmak(breaks_chord,coefs_chord,1);
for i = 1:length(breaks_chord)-1
fnplt(chord,[breaks_chord(i) breaks_chord(i+1)],'k')
hold on
end
I need to calculate the height h = c*t and plot h against the radial position.
How can I extract the c and t values at specific x-axis values (e.g. x=10, x=20, x=30)?
The functions 'findobj' and 'get' do not work.
Thanks in advance!

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回答（1 个）

Abhaya
Abhaya 2025-1-20
Hi,
To evaluate the values of 'chord' and 'thickness' at specific 'x' position, you can use MATLAB 'fnval' function.
Please refer to the steps given below to achieve this.
  • Use MATLAB 'fnval' function to evaluate the chord and thickness at your desired 'x' value:
c = fnval(chord,x);
t = fnval(thickness,x);
  • Calculate the height 'h' as the product of 'c' and 't':
h = c * t; % Calculate the height as the product of chord and thickness
For more details on using the fnval function, refer to the official MATLAB documentation:
https://www.mathworks.com/help/curvefit/fnval.html

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