File:Regression quadratique lineaire donnees gander.svg
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Summary[edit]
DescriptionRegression quadratique lineaire donnees gander.svg |
English: Fitting the data with a quadratic function (conic section). Data points from Gander, W., Golub, Gene, H. and Strebel, R., Least-Squares Fitting of Circles and Ellipses, BIT 34 (1994), 558-578.
The result is an ellipse.
Français : Régression par une fonction quadratique (conique). Nuage de points de Gander, W., Golub, Gene, H. and Strebel, R., Least-Squares Fitting of Circles and Ellipses, BIT 34 (1994), 558-578.
Le résultat est une ellipse. |
Date | |
Source | Own work |
Author | Cdang |
Parameters of the ellipse:
- cartesian equation: x2 + 0.815xy + 0.719y2 – 14.0x – 10.1 = 0;
- geometrical parameters:
- center C(5.38, 4.00),
- semi-axes: a = 2.80, b = 5.10,
- tilt: φ = 35.5°.
Scilab source
This media was created with Scilab, a free open-source software. Here is a listing of the Scilab source used to create this file. |
// **********
// Initialisation
// **********
clear;
// **********
// Données
// **********
X0 = [1, 2, 5, 7, 9, 6, 3, 8];
Y0 = [7, 6, 8, 7, 5, 7, 2, 4];
// **********
// Fonctions
// **********
function [a] = regression_quadratique(X, Y)
// méthode de la distance algébrique
// X, Y : points expérimentaux, matrices colonnes réelles
// a : coefficients de la formule quadratique (matrice colonne réelle)
YY = (X.*X);
XX = [(X.*Y) ; (Y.*Y) ; X ; Y];
[aa, b] = reglin(XX, YY);
a = [-aa, -b];
endfunction
function [phi]=trouve_rotation(A)
// A : coefficients de la formule quadratique (matrice colonne réelle)
// phi : angle que fait un axe de l'ellipse avec x (radians)
delta = 1 - 1/(1 + (A(3) - A(1))^2/A(2)^2);
absphi = acos(sqrt((1 + sqrt(delta))/2));
cap = cos(absphi); sap = sin(absphi);
signephi = sign(A(2)*(cap*cap - sap*sap)/(A(1) - A(3)));
phi = signephi*absphi;
endfunction
function [x,y]=trouve_centre(A)
// A : coefficients de la formule quadratique (matrice colonne réelle)
// x, y : coordonées du centre de l'ellipse (réels)
delta = A(2)*A(2) - 4*A(1)*A(3);
x = (2*A(3)*A(4) - A(2)*A(5))/delta;
y = (2*A(1)*A(5) - A(2)*A(4))/delta;
endfunction
function [rx, ry]=trouve_rayons(a, phi, xc, yc)
// a : coefficients de la formule quadratique (matrice colonne réelle)
// phi : angle que fait un axe de l'ellipse avec x
// xc, yc : coordonnées du centre de l'ellipse
// rx, ry : rayons (grand et petit demi-grands axes) de l'ellipse
A = [a(1), a(2)/2 ; a(2)/2, a(3)];
Q = rotate([1, 0 ; 0, 1], phi); // matrice de rotation
t = [xc ; yc]; // matrice de translation
Abar = Q'*A*Q;
b = [a(4) ; a(5)];
bbar = (2*t'*A + b')*Q;
c = a(6);
cbar = t'*A*t + b'*t + c;
rx = sqrt(abs(cbar/Abar(1,1)));
ry = sqrt(abs(cbar/Abar(2,2)));
endfunction
function [d]=conique(a, x, y)
d = a(1)*x'*x + a(2)*x'*y + a(3)*y'*y + a(4)*x + a(5)*y + a(6);
endfunction
function [] = trace_conique(a)
epsilon = 1.5e-1;
Xbase = 0:0.1:10;
Ybase = 1:0.1:9;
i = 1;
for x = Xbase
for y = Ybase
if abs(conique(a, x, y)) <= epsilon then
X(i) = x;
Y(i) = y;
i = i + 1;
end
end
end
Xmoy = mean(X); Ymoy = mean(Y); // détermination d'un point intérieur
theta = atan(Y-Ymoy, X-Xmoy); // angle des vecteurs
posMat = gsort([theta, X, Y], "lr"); // classement dans le sens trigo
[m, k] = max(abs(diff(posMat(:, 1)))); // saut de point
X = [posMat(k+1:$, 2) ; posMat(1:k, 2)]; // décalage circulaire
Y = [posMat(k+1:$, 3) ; posMat(1:k, 3)];
plot2d(X, Y, style = 5);
endfunction
// **********
// Programme principal
// **********
// lecture des données
Xdef = X0;
Ydef = Y0;
// Régression
Aopt = regression_quadratique(Xdef, Ydef);
aopt = [1, Aopt];
// affichage des paramètres
disp(aopt)
phi = trouve_rotation(aopt);
phideg = phi*180/%pi;
[xc, yc] = trouve_centre(aopt);
[a, b] = trouve_rayons(aopt, phi, xc, yc);
disp("phi = "+string(phi)+" rad = "+string(phideg)+"°.");
disp("C("+string(xc)+" ; "+string(yc)+").");
disp("a = "+string(a)+" ; b = "+string(b)+".");
// tracé
clf;
plot(Xdef, Ydef, "b+")
replot([0, 10 ; 1, 9]);
plot(xc, yc, "r+")
trace_conique(aopt)
Licensing[edit]
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Date/Time | Thumbnail | Dimensions | User | Comment | |
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current | 12:29, 24 May 2018 | 452 × 369 (27 KB) | Cdang (talk | contribs) | continuous line | |
10:10, 20 December 2012 | 452 × 364 (39 KB) | Cdang (talk | contribs) | {{Information |Description ={{en|1=Fitting the data with a quadratic function (conic section). Data points from Gander, W., Golub, Gene, H. and Strebel, R., ''Least-Squares Fitting of Circles and Ellipses'', BIT 34 (1994), 558-578. The result is an... |
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