Extract specific X & Y data from Contour curve

Question

Chinmayraj Doddarajappa 2022-8-25

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1786155-extract-specific-x-y-data-from-contour-curve

评论： Chinmayraj Doddarajappa 2022-8-25

Hello MATLAB experts,

I have this below contour plot. How can I get the X and Y coordinate data for the specific contour line 1. Either in an array or table format would do the job.

Thanks for looking at it. I have attached the script for the reference.

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Answer 1

Star Strider 2022-8-25

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1786155-extract-specific-x-y-data-from-contour-curve#answer_1033550

在 MATLAB Online 中打开

Try this —

%% Input Parameters for Earth

Ctheta = 5;

Cphi = 0.001;

phimax = deg2rad(58);

thetamax = deg2rad(45);

alpha = (pi/2)-thetamax;

H1 = hypergeom([2],[3/2,5/2],-thetamax^2);

H2 = hypergeom([2],[1/2,5/2],-thetamax^2);

g = 3.72;

rho = 0.0142;

ge = 9.81;

rhoe = 1.225;

r2 = 0.554;

r3 = 0.59;

Cl = 1.1;

Ct = Cl/sin(2*alpha);

Cd = Cl*tan(alpha);

%% Kolomenskiy Model for Earth Bee

R = 13.2*10^(-3);

c = 4.02*10^-3;

S = 2.*R.*c;

M = 175*10^-6;

mw = 0.2251*R^3;

W = M*g;

%% Kolomenskiy model for Mars Bee

nx = 75;

ny = 75;

Wm_var_out = [];

Klm_out = [];

Kpm_out = [];

Lavg_out =[];

AeroPower_out = [];

PosPinert_out = [];

Iyy_out = [];

N = linspace(1,6,nx);

f = linspace(155,1,ny);

for i = 1:nx

R1 = N(i).*R;

c1 = 0.273.*R1;

mw_var = 0.2251.*R1^3;

Mm_var = M+mw_var;

Wm_var = Mm_var.*g;

Wm_var_out=[Wm_var_out Wm_var];

for j=1:ny

%Average Lift

Klm = rho.*f(j).*(R1.^(2) *r2^(2)).*(2.*R1.*c1).*Ct;

Klm_out = [Klm_out Klm];

Lavg1 = Klm.*sin(2*alpha);

Lavg2 = ((Cphi/(asin(Cphi)))^(2) * (2*pi^(2).*f(j).*phimax^(2))./(1+sqrt(1-Cphi^(2))));

Lavg = Lavg1.*Lavg2;

Lavg_out = [Lavg_out Lavg];

%Average Aerodynamic Power

Kpm = rho.*f(j).*(R1.^(3) *r2^(3)).*(2.*R1.*c1).*(2*Ct);

Kpm_out = [Kpm_out Klm];

% Variation of Flapping Angle

T = 1./f(j);

t =(0:0.00001:T/2);

phi_t = (phimax/asin(Cphi)).*(asin(Cphi.*cos(2*pi.*f(j).*t)));

% Flapping Velocity

phidot_t = (phimax/asin(Cphi)).*((-2*pi.*f(j).*Cphi.*sin(2*pi.*f(j).*t))./sqrt(1-(Cphi^2.*(cos(2*pi.*f(j).*t)).^2)));

% Flapping Acceleration

phi2dot_t = ((4*pi^2 .*f(j).^2 *Cphi *phimax)./asin(Cphi)).*((((Cphi^2.*cos(2*pi.*f(j).*t).*sin(2*pi.*f(j).*t).^2)./(1-(Cphi^2.*cos(2*pi.*f(j).*t).^2)).^(3/2))-(cos(2*pi.*f(j).*t)./sqrt(1-(Cphi^2.*cos(2*pi.*f(j).*t).^2)))));

% Pitching Angle Time variation

theta_t = (thetamax/tanh(Ctheta)).*tanh(Ctheta.*sin(2*pi.*f(j).*t));

% Average Integral Aerodynamic Power

alpha_t = (pi/2)-theta_t;

Kpm = rho.*f(j).*(R1.^3 * r3^3).*(2.*R1.*c1)*(2*Ct);

Pa = phidot_t.^3.*(sin(alpha_t)).^2;

AeroPower = Kpm.*trapz(t,abs(Pa));

AeroPower_out = [AeroPower_out AeroPower];

Pa_I = Kpm.*abs(Pa);

% Inertial Power

Iyy = 0.0426.*R1.^5;

Iyy_out = [Iyy_out Iyy];

Pinert = phidot_t.*Iyy.*phi2dot_t;

B = find(Pinert>=0);

PosPinert = trapz(t(B),Pinert(B))/(T/4);

PosPinert_out = [PosPinert_out PosPinert];

end

Ptotal = AeroPower_out+PosPinert_out;

A = reshape(Lavg_out,ny,nx);

C = reshape(Ptotal,ny,nx);

SpecificLift = A./Wm_var_out;

figure

contourf(N,f,SpecificLift,'ShowText','on')

hold on

[M,C] = contourf(N,f,SpecificLift,[1 2 4 6 8 10 12 14 16 18 20],'ShowText','on');

colormap jet

colorbar

title('SF vs Freq vs Specific Lift')

xlabel('Scaling Factor')

ylabel('Frequency')

Levels = C.LevelList

Levels = 1×11

1 2 4 6 8 10 12 14 16 18 20

for k = 1:numel(Levels)

idx = find(M(1,:) == Levels(k));

ValidV = rem(M(2,idx),1) == 0;

StartIdx{k,:} = idx(ValidV);

VLen{k,:} = M(2,StartIdx{k});

end

figure

for k1 = 1:numel(Levels)

% k1 = 4; % Index For Levels 'k1'

hold on

for k2 = 1:numel(StartIdx{k1})

idxv = StartIdx{k1}(k2)+1 : StartIdx{k1}(k2)+VLen{k1}(k2); % Index For Contour 'k1'

xv = M(1,idxv);

yv = M(2,idxv);

plot(xv, yv)

end

hold off

hl = legend(compose('%2d',Levels), 'Location','best', 'NumColumns',2);

title(hl, 'Specific Lift')

xlabel('M(1,:)')

ylabel('M(2,:)')

% title(sprintf('Contour Level %.1f', Levels(k1)))

% axis('equal')

.

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Chinmayraj Doddarajappa 2022-8-25

Thank you,

Your code is working.

Can you please brief me what the code is doing to get the X and Y coordinated.

Star Strider 2022-8-25

As always, my pleasure!

The ‘xv’ and ‘yv’ values plot the curves for the ‘x’.and ‘y’ values respectively. Subscript them as:

xv{k1,k2} = M(1,idxv);

yv{k1,k2} = M(2,idxv);

where ‘k1’ are the indices of the levels (not the levels themselves), and ‘k2’ are the components of the contours (since in some contour plots, there may be several disconnected contours). For this contour plot, there should be only one (x,y) pair for each contour, so you can customise my code using only ‘k1’ for your contour plot.

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