圆拟合算法
参考转自 https://people.cas.uab.edu/~mosya/cl/CPPcircle.html
| Geometric circle fits |
Algebraic circle fits |
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Levenberg-Marquardt fit in the "full" (a,b,R) space https://people.cas.uab.edu/~mosya/cl/CircleFitByLevenbergMarquardtReduced.cpp https://people.cas.uab.edu/~mosya/cl/CircleFitByChernovLesort.cpp https://people.cas.uab.edu/~mosya/cl/CircleFitByChernovHoussam.cpp |
Kasa fit (the simplest and fastest fit, but biased toward smaller circles when an incomplete arc is observed) https://people.cas.uab.edu/~mosya/cl/CircleFitByKasa.cpp |
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Levenberg-Marquardt fit in the "full" (a,b,R) space
int CircleFitByLevenbergMarquardtFull (Data& data, Circle& circleIni, reals LambdaIni, Circle& circle)
/* <------------------ Input -------------------> <-- Output -->
Geometric circle fit to a given set of data points (in 2D)
Input: data - the class of data (contains the given points):
data.n - the number of data points
data.X[] - the array of X-coordinates
data.Y[] - the array of Y-coordinates
circleIni - parameters of the initial circle ("initial guess")
circleIni.a - the X-coordinate of the center of the initial circle
circleIni.b - the Y-coordinate of the center of the initial circle
circleIni.r - the radius of the initial circle
LambdaIni - the initial value of the control parameter "lambda"
for the Levenberg-Marquardt procedure
(common choice is a small positive number, e.g. 0.001)
Output:
integer function value is a code:
0: normal termination, the best fitting circle is
successfully found
1: the number of outer iterations exceeds the limit (99)
(indicator of a possible divergence)
2: the number of inner iterations exceeds the limit (99)
(another indicator of a possible divergence)
3: the coordinates of the center are too large
(a strong indicator of divergence)
circle - parameters of the fitting circle ("best fit")
circle.a - the X-coordinate of the center of the fitting circle
circle.b - the Y-coordinate of the center of the fitting circle
circle.r - the radius of the fitting circle
circle.s - the root mean square error (the estimate of sigma)
circle.i - the total number of outer iterations (updating the parameters)
circle.j - the total number of inner iterations (adjusting lambda)
Algorithm: Levenberg-Marquardt running over the full parameter space (a,b,r)
See a detailed description in Section 4.5 of the book by Nikolai Chernov:
"Circular and linear regression: Fitting circles and lines by least squares"
Chapman & Hall/CRC, Monographs on Statistics and Applied Probability, volume 117, 2010.
Nikolai Chernov, February 2014
*/
{
int code,i,iter,inner,IterMAX=99;
reals factorUp=10.,factorDown=0.04,lambda,ParLimit=1.e+6;
reals dx,dy,ri,u,v;
reals Mu,Mv,Muu,Mvv,Muv,Mr,UUl,VVl,Nl,F1,F2,F3,dX,dY,dR;
reals epsilon=3.e-8;
reals G11,G22,G33,G12,G13,G23,D1,D2,D3;
Circle Old,New;
// starting with the given initial circle (initial guess)
New = circleIni;
// compute the root-mean-square error via function Sigma; see Utilities.cpp
New.s = Sigma(data,New);
// initializing lambda, iteration counters, and the exit code
lambda = LambdaIni;
iter = inner = code = 0;
NextIteration:
Old = New;
if (++iter > IterMAX) {code = 1; goto enough;}
// computing moments
Mu=Mv=Muu=Mvv=Muv=Mr=0.;
for (i=0; i<data.n; i++)
{
dx = data.X[i] - Old.a;
dy = data.Y[i] - Old.b;
ri = sqrt(dx*dx + dy*dy);
u = dx/ri;
v = dy/ri;
Mu += u;
Mv += v;
Muu += u*u;
Mvv += v*v;
Muv += u*v;
Mr += ri;
}
Mu /= data.n;
Mv /= data.n;
Muu /= data.n;
Mvv /= data.n;
Muv /= data.n;
Mr /= data.n;
// computing matrices
F1 = Old.a + Old.r*Mu - data.meanX;
F2 = Old.b + Old.r*Mv - data.meanY;
F3 = Old.r - Mr;
Old.g = New.g = sqrt(F1*F1 + F2*F2 + F3*F3);
try_again:
UUl = Muu + lambda;
VVl = Mvv + lambda;
Nl = One + lambda;
// Cholesly decomposition
G11 = sqrt(UUl);
G12 = Muv/G11;
G13 = Mu/G11;
G22 = sqrt(VVl - G12*G12);
G23 = (Mv - G12*G13)/G22;
G33 = sqrt(Nl - G13*G13 - G23*G23);
D1 = F1/G11;
D2 = (F2 - G12*D1)/G22;
D3 = (F3 - G13*D1 - G23*D2)/G33;
dR = D3/G33;
dY = (D2 - G23*dR)/G22;
dX = (D1 - G12*dY - G13*dR)/G11;
if ((abs(dR)+abs(dX)+abs(dY))/(One+Old.r) < epsilon) goto enough;
// updating the parameters
New.a = Old.a - dX;
New.b = Old.b - dY;
if (abs(New.a)>ParLimit || abs(New.b)>ParLimit) {code = 3; goto enough;}
New.r = Old.r - dR;
if (New.r <= 0.)
{
lambda *= factorUp;
if (++inner > IterMAX) {code = 2; goto enough;}
goto try_again;
}
// compute the root-mean-square error via function Sigma; see Utilities.cpp
New.s = Sigma(data,New);
// check if improvement is gained
if (New.s < Old.s) // yes, improvement
{
lambda *= factorDown;
goto NextIteration;
}
else // no improvement
{
if (++inner > IterMAX) {code = 2; goto enough;}
lambda *= factorUp;
goto try_again;
}
// exit
enough:
Old.i = iter; // total number of outer iterations (updating the parameters)
Old.j = inner; // total number of inner iterations (adjusting lambda)
circle = Old;
return code;
}Levenberg-Marquardt fit in the "reduced" (a,b) space
int CircleFitByLevenbergMarquardtReduced (Data& data, Circle& circleIni, reals LambdaIni, Circle& circle)
/* <------------------ Input -------------------> <-- Output -->
Geometric circle fit to a given set of data points (in 2D)
Input: data - the class of data (contains the given points):
data.n - the number of data points
data.X[] - the array of X-coordinates
data.Y[] - the array of Y-coordinates
circleIni - parameters of the initial circle ("initial guess")
circleIni.a - the X-coordinate of the center of the initial circle
circleIni.b - the Y-coordinate of the center of the initial circle
circleIni.r - the radius of the initial circle
LambdaIni - the initial value of the control parameter "lambda"
for the Levenberg-Marquardt procedure
(common choice is a small positive number, e.g. 0.001)
Output:
integer function value is a code:
0: normal termination, the best fitting circle is
successfully found
1: the number of outer iterations exceeds the limit (99)
(indicator of a possible divergence)
2: the number of inner iterations exceeds the limit (99)
(another indicator of a possible divergence)
3: the coordinates of the center are too large
(a strong indicator of divergence)
circle - parameters of the fitting circle ("best fit")
circle.a - the X-coordinate of the center of the fitting circle
circle.b - the Y-coordinate of the center of the fitting circle
circle.r - the radius of the fitting circle
circle.s - the root mean square error (the estimate of sigma)
circle.i - the total number of outer iterations (updating the parameters)
circle.j - the total number of inner iterations (adjusting lambda)
Algorithm: Levenberg-Marquardt running over the "reduced" parameter space (a,b)
(the radius r is always set to its optimal value)
See a detailed description in Section 4.6 of the book by Nikolai Chernov:
"Circular and linear regression: Fitting circles and lines by least squares"
Chapman & Hall/CRC, Monographs on Statistics and Applied Probability, volume 117, 2010.
Nikolai Chernov, February 2014
*/
{
int code,i,pivot,iter,inner,IterMAX=99;
reals factorUp=10.,factorDown=0.04,lambda,ParLimit=1.e+6;
reals dx,dy,ri,u,v;
reals Mu,Mv,Muu,Mvv,Muv,Mr,A11,A12,A22,F1,F2,dX,dY;
reals epsilon=3.e-8;
reals G11,G12,G22,D1,D2;
Circle Old,New;
data.means(); // Compute x- and y-means (via a function in class "data")
// starting with the given initial circle (initial guess)
New = circleIni;
// compute the root-mean-square error via function SigmaReduced; see Utilities.cpp
New.s = SigmaReduced(data,New);
// initializing lambda, iteration counters, and the exit code
lambda = LambdaIni;
iter = inner = code = 0;
NextIteration:
Old = New;
if (++iter > IterMAX) {code = 1; goto enough;}
// computing moments
Mu=Mv=Muu=Mvv=Muv=Mr=0.;
for (i=0; i<data.n; i++)
{
dx = data.X[i] - Old.a;
dy = data.Y[i] - Old.b;
ri = sqrt(dx*dx + dy*dy);
u = dx/ri;
v = dy/ri;
Mu += u;
Mv += v;
Muu += u*u;
Mvv += v*v;
Muv += u*v;
Mr += ri;
}
Mu /= data.n;
Mv /= data.n;
Muu /= data.n;
Mvv /= data.n;
Muv /= data.n;
Mr /= data.n;
// computing matrices
F1 = Old.a + Mu*Mr - data.meanX;
F2 = Old.b + Mv*Mr - data.meanY;
try_again:
A11 = (Muu - Mu*Mu) + lambda;
A22 = (Mvv - Mv*Mv) + lambda;
A12 = Muv - Mu*Mv;
if (A11<epsilon || A22<epsilon || A11*A22-A12*A12<epsilon)
{
lambda *= factorUp;
goto try_again;
}
// Cholesky decomposition with pivoting
pivot=0;
if (A11 < A22)
{
swap(A11,A22);
swap(F1,F2);
pivot=1;
}
G11 = sqrt(A11);
G12 = A12/G11;
G22 = sqrt(A22 - G12*G12);
D1 = F1/G11;
D2 = (F2 - G12*D1)/G22;
// updating the parameters
dY = D2/G22;
dX = (D1 - G12*dY)/G11;
if ((abs(dX)+abs(dY))/(One+abs(Old.a)+abs(Old.b)) < epsilon) goto enough;
if (pivot != 0) swap(dX,dY);
New.a = Old.a - dX;
New.b = Old.b - dY;
if (abs(New.a)>ParLimit || abs(New.b)>ParLimit) {code = 3; goto enough;}
// compute the root-mean-square error via function SigmaReduced; see Utilities.cpp
New.s = SigmaReduced(data,New);
// check if improvement is gained
if (New.s < Old.s) // yes, improvement
{
lambda *= factorDown;
goto NextIteration;
}
else // no improvement
{
if (++inner > IterMAX) {code = 2; goto enough;}
lambda *= factorUp;
goto try_again;
}
// exit
enough:
// compute the optimal radius via a function in Utilities.cpp
Old.r = OptimalRadius(data,Old);
Old.i = iter;
Old.j = inner;
circle = Old;
return code;
}Chernov-Lesort fit
int CircleFitByChernovLesort (Data& data, Circle& circleIni, reals LambdaIni, Circle& circle)
/* <------------------ Input -------------------> <-- Output -->
Geometric circle fit to a given set of data points (in 2D)
Input: data - the class of data (contains the given points):
data.n - the number of data points
data.X[] - the array of X-coordinates
data.Y[] - the array of Y-coordinates
circleIni - parameters of the initial circle ("initial guess")
circleIni.a - the X-coordinate of the center of the initial circle
circleIni.b - the Y-coordinate of the center of the initial circle
circleIni.r - the radius of the initial circle
LambdaIni - the initial value of the control parameter "lambda"
for the Levenberg-Marquardt procedure
(common choice is a small positive number, e.g. 0.001)
Output:
integer function value is a code:
0: normal termination, the best fitting circle is
successfully found
1: the number of outer iterations exceeds the limit (99)
(indicator of a possible divergence)
2: the number of inner iterations exceeds the limit (99)
(another indicator of a possible divergence)
3: the coordinates of the center are too large
(a strong indicator of divergence)
circle - parameters of the fitting circle ("best fit")
circle.a - the X-coordinate of the center of the fitting circle
circle.b - the Y-coordinate of the center of the fitting circle
circle.r - the radius of the fitting circle
circle.s - the root mean square error (the estimate of sigma)
circle.i - the total number of outer iterations (updating the parameters)
circle.j - the total number of inner iterations (adjusting lambda)
Algorithm by Nikolai Chernov and Claire Lesort
See a detailed description in the journal paper:
N. Chernov and C. Lesort, "Least squares fitting of circles"
in J. Math. Imag. Vision, volume 23, (2005), pages 239-251.
the algorithm is designed to converge from any initial guess,
but it is complicated and generally very slow
Nikolai Chernov, February 2014
*/
{
int code,i,iter,inner,IterMAX=99;
reals factorUp=10.,factorDown=0.04,lambda;
reals Aold,Fold,Told,Anew,Fnew,Tnew,DD,H,aabb;
reals Xi,Yi,Zi,Ui,Vi,Gi,CT,ST,D,ADF,SQ,DEN,FACT,DGDAi,DGDFi,DGDTi;
reals H11,H12,H13,H22,H23,H33,F1,F2,F3,dA,dF,dT;
reals epsilon=3.e-8;
reals G11,G22,G33,G12,G13,G23,D1,D2,D3;
reals Xshift=0.,Yshift=0.,dX=One,dY=0.,aTemp,bTemp,rTemp;
Circle Old,New;
// starting with the given initial circle (initial guess)
New = circleIni;
// compute the root-mean-square error via function Sigma; see Utilities.cpp
New.s = Sigma(data,New);
Anew = One/Two/New.r;
aabb = New.a*New.a + New.b*New.b;
Fnew = (aabb - New.r*New.r)*Anew;
Tnew = acos(-New.a/sqrt(aabb));
if (New.b > 0.) Tnew = Two*Pi - Tnew;
if (One+Four*Anew*Fnew < epsilon)
{
Xshift += dX;
Yshift += dY;
New.a += dX;
New.b += dY;
aabb = New.a*New.a + New.b*New.b;
Fnew = (aabb - New.r*New.r)*Anew;
Tnew = acos(-New.a/sqrt(aabb));
if (New.b > 0.) Tnew = Two*Pi - Tnew;
}
// initializing lambda, iteration counters, and the exit code
lambda = LambdaIni;
iter = inner = code = 0;
NextIteration:
Aold = Anew;
Fold = Fnew;
Told = Tnew;
Old = New;
if (++iter > IterMAX) {code = 1; goto enough;}
// computing moments
shiftXY:
DD = One + Four*Aold*Fold;
D = sqrt(DD);
CT = cos(Told);
ST = sin(Told);
H11=H12=H13=H22=H23=H33=F1=F2=F3=0.;
for (i=0; i<data.n; i++)
{
Xi = data.X[i] + Xshift;
Yi = data.Y[i] + Yshift;
Zi = Xi*Xi + Yi*Yi;
Ui = Xi*CT + Yi*ST;
Vi =-Xi*ST + Yi*CT;
ADF = Aold*Zi + D*Ui + Fold;
SQ = sqrt(Four*Aold*ADF + One);
DEN = SQ + One;
Gi = Two*ADF/DEN;
FACT = Two/DEN*(One - Aold*Gi/SQ);
DGDAi = FACT*(Zi + Two*Fold*Ui/D) - Gi*Gi/SQ;
DGDFi = FACT*(Two*Aold*Ui/D + One);
DGDTi = FACT*D*Vi;
H11 += DGDAi*DGDAi;
H12 += DGDAi*DGDFi;
H13 += DGDAi*DGDTi;
H22 += DGDFi*DGDFi;
H23 += DGDFi*DGDTi;
H33 += DGDTi*DGDTi;
F1 += Gi*DGDAi;
F2 += Gi*DGDFi;
F3 += Gi*DGDTi;
}
Old.g = New.g = sqrt(F1*F1 + F2*F2 + F3*F3);
try_again:
// Cholesky decomposition
G11 = sqrt(H11 + lambda);
G12 = H12/G11;
G13 = H13/G11;
G22 = sqrt(H22 + lambda - G12*G12);
G23 = (H23 - G12*G13)/G22;
G33 = sqrt(H33 + lambda - G13*G13 - G23*G23);
D1 = F1/G11;
D2 = (F2 - G12*D1)/G22;
D3 = (F3 - G13*D1 - G23*D2)/G33;
dT = D3/G33;
dF = (D2 - G23*dT)/G22;
dA = (D1 - G12*dF - G13*dT)/G11;
// updating the parameters
Anew = Aold - dA;
Fnew = Fold - dF;
Tnew = Told - dT;
if (One+Four*Anew*Fnew < epsilon)
{
Xshift += dX;
Yshift += dY;
H = sqrt(One+Four*Aold*Fold);
aTemp = -H*cos(Told)/(Aold+Aold) + dX;
bTemp = -H*sin(Told)/(Aold+Aold) + dY;
rTemp = One/abs(Aold+Aold);
Aold = One/(rTemp + rTemp);
aabb = aTemp*aTemp + bTemp*bTemp;
Fold = (aabb - rTemp*rTemp)*Aold;
Told = acos(-aTemp/sqrt(aabb));
if (bTemp > 0.) Told = Two*Pi - Told;
lambda *= factorUp;
inner++;
goto shiftXY;
}
H = sqrt(One+Four*Anew*Fnew);
New.a = -H*cos(Tnew)/(Anew+Anew) - Xshift;
New.b = -H*sin(Tnew)/(Anew+Anew) - Yshift;
New.r = One/abs(Anew+Anew);
New.s = Sigma(data,New);
if ((abs(New.a-Old.a) + abs(New.b-Old.b) + abs(New.r-Old.r))/(One + Old.r) < epsilon) goto enough;
// check if improvement is gained
if (New.s < Old.s) // yes, improvement
{
lambda *= factorDown;
goto NextIteration;
}
else // no improvement
{
if (++inner > IterMAX) {code = 2; goto enough;}
lambda *= factorUp;
goto try_again;
}
// exit
enough:
Old.i = iter;
Old.j = inner;
circle = Old;
return code;
}
//****************** Perturb *********************************
Circle Perturb (Circle& New, Circle& Old, reals range)
{
Circle Perturbed;
if (range==0.) return New;
Perturbed.a = New.a + (New.a - Old.a)*(range*rand()/RAND_MAX - range/Two);
Perturbed.b = New.b + (New.b - Old.b)*(range*rand()/RAND_MAX - range/Two);
Perturbed.r = New.r + (New.r - Old.r)*(range*rand()/RAND_MAX - range/Two);
return Perturbed;
}
Chernov-Houssam fit
void eigen2x2(reals a, reals b, reals c, reals& d1, reals& d2, reals& Vx, reals& Vy)
/* <------- Input ----------> <--------------- Output ----------------->
Eigendecomposition of a symmetric 2x2 matrix
faster and more accurate than the library function
Input: a,b,c - components of the matrix [a c
c b]
Output: d1,d2 - eigenvalues
Vx,Vy - unit eigenvector for d1
The eigenvector for d2 need not be computed, it is (-Vy,Vx)
Note: d1 is the leading eigenvalue, i.e., |d1|>=|d2|
Nikolai Chernov, June 2012
*/
{
reals disc,f;
disc = pythag(a-b,Two*c); // discriminant
d1 = (a+b > 0.) ? (a + b + disc)/Two : (a + b - disc)/Two;
d2 = (a*b - c*c)/d1;
if (abs(a-d1) > abs(b-d1))
{
if ((f=pythag(c,d1-a))==0.)
{
Vx = One; Vy = 0.; return;
}
else
{
Vx = c/f; Vy = (d1-a)/f;
}
}
else
{
if ((f=pythag(c,d1-b))==0.)
{
Vx = One; Vy = 0.; return;
}
else
{
Vx = (d1-b)/f; Vy = c/f;
}
}
return;
}
reals SigmaWithLargeCircleOption (Data& data, Circle& circle)
/* <-------- Input --------->
Compute the objective function for the geometric circle fitting problem
Input: data - the class of data (contains the given points):
data.n - the number of data points
data.X[] - the array of X-coordinates
data.Y[] - the array of Y-coordinates
data.meanX - the mean X-coordinate
data.meanY - the mean Y-coordinate
(the last two must be precomputed)
circle - the class of circle parameters:
circle.a - the X-coordinate of the center
circle.b - the Y-coordinate of the center
Output:
the value of the objective function
(more precisely, the square root of the average square of the distance)
Nikolai Chernov, January 2013
*/
{
int i,n=data.n;
reals sum=0.,dx,dy,r,D[n];
reals LargeCircle=Ten,a0,b0,del,s,c,x,y,z,p,t,g,W,Z;
if (abs(circle.a)<LargeCircle && abs(circle.b)<LargeCircle) // main case (not a large circle)
{
for (i=0; i<n; i++)
{
dx = data.X[i] - circle.a;
dy = data.Y[i] - circle.b;
D[i] = sqrt(dx*dx+dy*dy);
sum += D[i];
}
r = sum/n;
for (sum=0., i=0; i<n; i++) sum += SQR(D[i] - r);
return sum/n;
}
else // case of a large circle
{
a0 = circle.a-data.meanX; b0 = circle.b-data.meanY;
del = One/sqrt(a0*a0 + b0*b0);
s = b0*del; c = a0*del;
for (W=Z=0.,i=0; i<n; i++)
{
x = data.X[i] - data.meanX;
y = data.Y[i] - data.meanY;
z = x*x + y*y;
p = x*c + y*s;
t = del*z - Two*p;
g = t/(One+sqrt(One+del*t));
W += (z+p*g)/(Two+del*g);
Z += z;
}
W /= n;
Z /= n;
return Z-W*(Two+del*del*W);
}
}
void GradientHessian (Data& data, Circle& circle, reals& F1, reals& F2, reals& A11, reals& A22, reals& A12)
/* <-------- Input ---------> <----------------------- Output ----------------------->
Compute the gradient vector and the Hessian matrix of the objective function
for the geometric circle fitting problem
Input: data - the class of data (contains the given points):
data.n - the number of data points
data.X[] - the array of X-coordinates
data.Y[] - the array of Y-coordinates
data.meanX - the mean X-coordinate
data.meanY - the mean Y-coordinate
(the last two must be precomputed)
circle - the class of circle parameters:
circle.a - the X-coordinate of the center
circle.b - the Y-coordinate of the center
Output:
[F1 F2] - the coordinates of the gradient vector
A11 A12 - the components of the Hessian matrix
A12 A22 (it is symmetric, so only three are computed)
Nikolai Chernov, January 2013
*/
{
int i,n=data.n;
reals LargeCircle=Ten,dx,dy,r,u,v,Mr,Mu,Mv,Muu,Mvv,Muv,Muur,Mvvr,Muvr;
reals a0,b0,del,dd,s,c,x,y,a,b,z,p,t,w,g,g1,gg1,gg2;
reals X,Y,R,U,V,T,W,AA,BB,AB,AG,BG,GG,UUR,VVR,UVR;
if (abs(circle.a)<LargeCircle && abs(circle.b)<LargeCircle) // main case (not a large circle)
{
for (Mr=Mu=Mv=Muu=Mvv=Muv=Muur=Mvvr=Muvr=0.,i=0; i<n; i++)
{
dx = data.X[i] - circle.a;
dy = data.Y[i] - circle.b;
r = sqrt(dx*dx + dy*dy);
u = dx/r;
v = dy/r;
Mr += r;
Mu += u;
Mv += v;
Muu += u*u;
Mvv += v*v;
Muv += u*v;
Muur += u*u/r;
Mvvr += v*v/r;
Muvr += u*v/r;
}
Mr /= n;
Mu /= n;
Mv /= n;
Muu /= n;
Mvv /= n;
Muv /= n;
Muur /= n;
Mvvr /= n;
Muvr /= n;
F1 = circle.a + Mu*Mr - data.meanX;
F2 = circle.b + Mv*Mr - data.meanY;
A11 = One - Mu*Mu - Mr*Mvvr;
A22 = One - Mv*Mv - Mr*Muur;
A12 = -Mu*Mv + Mr*Muvr;
}
else // case of a large circle
{
a0 = circle.a-data.meanX; b0 = circle.b-data.meanY;
del = One/sqrt(a0*a0 + b0*b0); dd = del*del;
s = b0*del; c = a0*del;
for (X=Y=R=T=W=AA=BB=AB=AG=BG=GG=0.,i=0; i<n; i++)
{
x = data.X[i] - data.meanX;
y = data.Y[i] - data.meanY;
z = x*x + y*y;
p = x*c + y*s;
t = Two*p-del*z;
w = sqrt(One-del*t);
g = -t/(One+w);
g1 = One/(One+del*g);
gg1 = g*g1;
gg2 = g/(Two+del*g);
a = (x+g*c)/w;
b = (y+g*s)/w;
X += x*gg1;
Y += y*gg1;
R += z + t*gg2;
T += t*gg1;
W += t*gg1*gg2;
AA += a*a*g1;
BB += b*b*g1;
AB += a*b*g1;
AG += a*gg1;
BG += b*gg1;
GG += g*gg1;
}
X /= n;
Y /= n;
R /= n;
T /= n;
W /= n;
AA /= n;
BB /= n;
AB /= n;
AG /= n;
BG /= n;
GG /= n;
U = (T-del*W)*c/Two - X + R*c/Two;
V = (T-del*W)*s/Two - Y + R*s/Two;
// compute the components of the gradient vector
F1 = del*((dd*R*U - del*W*c + T*c)/Two - X);
F2 = del*((dd*R*V - del*W*s + T*s)/Two - Y);
UUR = ((GG-R/Two)*c + Two*(AG-U))*c + AA;
VVR = ((GG-R/Two)*s + Two*(BG-V))*s + BB;
UVR = ((GG-R/Two)*c + (AG-U))*s + (BG-V)*c + AB;
// compute the components of the Hessian matrix
A11 = dd*(U*(Two*c - dd*U) - R*s*s/Two - VVR*(One + dd*R/Two));
A22 = dd*(V*(Two*s - dd*V) - R*c*c/Two - UUR*(One + dd*R/Two));
A12 = dd*(U*s + V*c + R*s*c/Two - dd*U*V + UVR*(One + dd*R/Two));
}
}
int CircleFitByChernovHoussam (Data& data, Circle& circleIni, reals LambdaIni, Circle& circle)
/* <------------------ Input -------------------> <-- Output -->
Geometric circle fit to a given set of data points (in 2D)
Input: data - the class of data (contains the given points):
data.n - the number of data points
data.X[] - the array of X-coordinates
data.Y[] - the array of Y-coordinates
circleIni - parameters of the initial circle ("initial guess")
circleIni.a - the X-coordinate of the center of the initial circle
circleIni.b - the Y-coordinate of the center of the initial circle
circleIni.r - the radius of the initial circle
LambdaIni - the initial value of the control parameter "lambda"
for the Levenberg-Marquardt procedure
(common choice is a small positive number, e.g. 0.001)
Output:
integer function value is a code:
0: normal termination, the best fitting circle is
successfully found
1: the number of outer iterations exceeds the limit (99)
(indicator of a possible divergence)
2: the number of inner iterations exceeds the limit (99)
(another indicator of a possible divergence)
3: convergence to a point where the Hessian matrix
is NOT positive definite. This indicates that
the fitting circle may correspond to a maximum
or to a saddle point of the objective function
circle - parameters of the fitting circle ("best fit")
circle.a - the X-coordinate of the center of the fitting circle
circle.b - the Y-coordinate of the center of the fitting circle
circle.r - the radius of the fitting circle
circle.s - the root mean square error (the estimate of sigma)
circle.i - the total number of outer iterations (updating the parameters)
circle.j - the total number of inner iterations (adjusting lambda)
Algorithm is based on the paper by H. Abdul-Rahman and N. Chernov
"Fast and numerically stable circle fit"
in Journal of Mathematical Imaging and Vision (2013)
Nikolai Chernov, January 2013
*/
{
int i,n=data.n,iter,inner,IterMAX=200,check_line=1,code;
reals lambda;
reals F1,F2,A11,A22,A12,dX,dY,Mxx,Myy,Mxy,Mxxy,dx,dy;
reals d1,d2,dmin=One,Vx,Vy,dL1,dL2,VLx,VLy,aL,bL,R,G1,G2,sBest,gBest,AB,progress;
// control parameters (have been optimized empirically):
reals ParLimit2=100.;
reals epsilon=1.e+7*REAL_EPSILON;;
reals factor1=32.,factor2=32.;
reals ccc=0.4;
reals factorUp=10.,factorDown=0.1;
Circle Old,New;
data.means(); // Compute x- and y-means (via a function in class "data")
// starting with the given initial guess
New = circleIni; // initialize the circle
New.s = SigmaWithLargeCircleOption(data,New); // compute the root-mean-square error
GradientHessian(data,New,F1,F2,A11,A22,A12); // compute the gradient vector and Hessian matrix
New.Gx = F1; New.Gy = F2; New.g = sqrt(F1*F1 + F2*F2); // the gradient vector and its norm
lambda = LambdaIni; // initialize lambda
iter = inner = code = 0; // initialize iteration counters and the exit code
sBest = gBest = progress = REAL_MAX; // set control variables to LARGE values
//if (lpr==1) cout << iter <<" ("<<New.a<<","<<New.b<<") s="<<New.s<<" g="<< New.g<<" L="<<lambda << endl;
NextIteration: // starting point of the current iteration of Newton's method
if (iter>0) progress = (abs(New.a-Old.a)+abs(New.b-Old.b))/(SQR(Old.a)+SQR(Old.b)+One);
// evaluate the progress made during the previous iteration
Old = New;
if (++iter > IterMAX) goto enough; // termination due to going over the limit
eigen2x2(A11,A22,A12,d1,d2,Vx,Vy); // eigendecomposition of the Hessian matrix
dmin = (d1<d2) ? d1 : d2; // recording the smaller e-value
AB=sqrt(SQR(Old.a)+SQR(Old.b)) + One; // approximation to the circle size
// main stopping rule: terminate iterations if
// the gradient vector is small enough and the progress is not substantial
if ((Old.g < factor1*REAL_EPSILON)&&(progress<epsilon))
{
//if (lpr==1) cout << "++++ gradient is small enough ++++" << endl;
goto enough;
}
// secondary stopping rule (prevents some stupid cycling)
if ((Old.s >= sBest)&&(Old.g >= gBest))
{
//if (lpr==1) cout << "++++ iterations stabilize (best results repeated) ++++" << endl;
goto enough;
}
if (sBest > Old.s) sBest = Old.s; // updating the smallest value of the objective function found so far
if (gBest > Old.g) gBest = Old.g; // updating the smallest length of the gradient vector found so far
G1 = Vx*F1 + Vy*F2; // rotating the gradient vector
G2 = Vx*F2 - Vy*F1; // (expressing it in the eigensystem of the Hessian matrix)
try_again: // starting point of an "inner" iteration (adjusting lambda)
// enforcing a lower bound on lambda that guarantees that
// (i) the augmented Hessian matrix is positive definite
// (ii) the step is not too big (does not exceed a certain fraction of the circle size)
// the fraction is defined by the factor "ccc")
if (lambda < abs(G1)/AB/ccc - d1) lambda = abs(G1)/AB/ccc - d1;
if (lambda < abs(G2)/AB/ccc - d2) lambda = abs(G2)/AB/ccc - d2;
// computing the step (dX,dY) by using the current va;ue of lambda
dX = Old.Gx*(Vx*Vx/(d1+lambda)+Vy*Vy/(d2+lambda)) + Old.Gy*Vx*Vy*(One/(d1+lambda)-One/(d2+lambda));
dY = Old.Gx*Vx*Vy*(One/(d1+lambda)-One/(d2+lambda)) + Old.Gy*(Vx*Vx/(d2+lambda)+Vy*Vy/(d1+lambda));
// updating the circle parameters
New.a = Old.a - dX;
New.b = Old.b - dY;
if ((New.a==Old.a)&&(New.b==Old.b)) // if no change, terminate iterations
{
//if (lpr==1) cout << "++++ iterations stabilize (no change in center) ++++" << endl;
goto enough;
}
// check if the circle is very large
if (abs(New.a)>ParLimit2 || abs(New.b)>ParLimit2)
{
// when the circle is very large for the first time, check if
// the best fitting line gives the best fit
if (check_line) // initially, check_line=1, then it is set to zero
{
//if (lpr==1) cout << " Linear zone 1st iter=" << iter << " (" << New.a << "," << New.b << ")" << endl;
// compute scatter matrix
for (Mxx=Myy=Mxy=0.,i=0; i<n; i++)
{
dx = data.X[i] - data.meanX;
dy = data.Y[i] - data.meanY;
Mxx += dx*dx;
Myy += dy*dy;
Mxy += dx*dy;
}
eigen2x2(Mxx,Myy,Mxy,dL1,dL2,VLx,VLy); // eigendecomposition of scatter matrix
// compute the third mixed moment (after rotation of coordinates)
for (Mxxy=0.,i=0; i<n; i++)
{
dx = (data.X[i] - data.meanX)*VLx + (data.Y[i] - data.meanY)*VLy;
dy = (data.Y[i] - data.meanY)*VLx - (data.X[i] - data.meanX)*VLy;
Mxxy += dx*dx*dy;
}
// check if the line is the best fit
//if (Mxxy == 0.) { cout << " Line " << endl; cin.ignore(); } // need to finish this block...
// rough estimate of the center to be used later to recoved from the wrong valley
R = (Mxxy>0.) ? ParLimit2 : -ParLimit2;
aL = -VLy*R;
bL = VLx*R;
check_line = 0; // set to zero to prevent further checks for line
}
if ((New.a*VLy - New.b*VLx)*R>0.) // check if the circle is in the wrong valley
{
//if (lpr==1) cout << " Linear zone foul iter=" << iter << " (" << New.a << "," << New.b << ")" << endl;
New.a = aL; // switch to the rough circle estimate
New.b = bL; // (precomupted earlier)
New.s = SigmaWithLargeCircleOption(data,New); // compute the root-mean-square error
GradientHessian(data,New,F1,F2,A11,A22,A12); // compute the gradient vector and Hessian matrix
New.Gx = F1; New.Gy = F2; New.g = sqrt(F1*F1 + F2*F2); // the gradient vector and its norm
lambda = LambdaIni; // reset lambda
sBest = gBest = REAL_MAX; // reset best circle characteristics
//if (lpr==1) cout << " Linear zone flip iter=" << iter << " (" << New.a << "," << New.b << ")" << endl;
goto NextIteration; // restart the Newton's iteration
}
}
New.s = SigmaWithLargeCircleOption(data,New); // compute the root-mean-square error
GradientHessian(data,New,F1,F2,A11,A22,A12); // compute the gradient vector and Hessian matrix
New.Gx = F1; New.Gy = F2; New.g = sqrt(F1*F1 + F2*F2); // the gradient vector and its norm
//if (lpr==1) cout << setprecision(15)<<iter <<" ("<<New.a<<","<<New.b<<" s="<<New.s<<" g="<< New.g<<" L="<<lambda<<endl;
// check if improvement is gained
if (New.s < sBest*(One+factor2*REAL_EPSILON)) // yes, improvement
{
lambda *= factorDown; // reduce lambda
goto NextIteration; // proceed to the next Newton's iteration
}
else // no improvement
{
//if (lpr==1) cout << " repeat with higher lambda" << endl;
if (++inner > IterMAX) goto enough; // termination due to going over the limit
lambda = factorUp*lambda; // increace lambda
goto try_again; // make another inner iteration
}
enough: // exit
Old.r = OptimalRadius(data,Old);
Old.i = iter;
Old.j = inner;
circle = Old; // output circle class
if (iter > IterMAX) code = 1; // error code set to 1
if (inner > IterMAX) code = 2; // error code set to 2
if ((dmin <= 0.)&&(code==0))
{
//cout << " negative e-value=" << setprecision(20) << dmin << " iter=" << iter <<" ("<<Old.a<<","<<Old.b<< ")" << endl;
code = 3; // error code set to 3
}
return code;
}Kasa fit
Circle CircleFitByKasa (Data& data)
/*
Circle fit to a given set of data points (in 2D)
This is an algebraic fit, disovered and rediscovered by many people.
One of the earliest publications is due to Kasa:
I. Kasa, "A curve fitting procedure and its error analysis",
IEEE Trans. Inst. Meas., Vol. 25, pages 8-14, (1976)
Input: data - the class of data (contains the given points):
data.n - the number of data points
data.X[] - the array of X-coordinates
data.Y[] - the array of Y-coordinates
Output:
circle - parameters of the fitting circle:
circle.a - the X-coordinate of the center of the fitting circle
circle.b - the Y-coordinate of the center of the fitting circle
circle.r - the radius of the fitting circle
circle.s - the root mean square error (the estimate of sigma)
circle.j - the total number of iterations
The method is based on the minimization of the function
F = sum [(x-a)^2 + (y-b)^2 - R^2]^2
This is perhaps the simplest and fastest circle fit.
It works well when data points are sampled along an entire circle
or a large part of it (at least half circle).
It does not work well when data points are sampled along a small arc
of a circle. In that case the method is heavily biased, it returns
circles that are too often too small.
It is the oldest algebraic circle fit (first published in 1972?).
For 20-30 years it has been the most popular circle fit, at least
until the more robust Pratt fit (1987) and Taubin fit (1991) were invented.
Nikolai Chernov (September 2012)
*/
{
int i;
reals Xi,Yi,Zi;
reals Mxy,Mxx,Myy,Mxz,Myz;
reals B,C,G11,G12,G22,D1,D2;
Circle circle;
data.means(); // Compute x- and y- sample means (via a function in the class "data")
// computing moments
Mxx=Myy=Mxy=Mxz=Myz=0.;
for (i=0; i<data.n; i++)
{
Xi = data.X[i] - data.meanX; // centered x-coordinates
Yi = data.Y[i] - data.meanY; // centered y-coordinates
Zi = Xi*Xi + Yi*Yi;
Mxx += Xi*Xi;
Myy += Yi*Yi;
Mxy += Xi*Yi;
Mxz += Xi*Zi;
Myz += Yi*Zi;
}
Mxx /= data.n;
Myy /= data.n;
Mxy /= data.n;
Mxz /= data.n;
Myz /= data.n;
// solving system of equations by Cholesky factorization
G11 = sqrt(Mxx);
G12 = Mxy/G11;
G22 = sqrt(Myy - G12*G12);
D1 = Mxz/G11;
D2 = (Myz - D1*G12)/G22;
// computing paramters of the fitting circle
C = D2/G22/Two;
B = (D1 - G12*C)/G11/Two;
// assembling the output
circle.a = B + data.meanX;
circle.b = C + data.meanY;
circle.r = sqrt(B*B + C*C + Mxx + Myy);
circle.s = Sigma(data,circle);
circle.i = 0;
circle.j = 0;
return circle;
}Pratt fit
Circle CircleFitByPratt (Data& data)
/*
Circle fit to a given set of data points (in 2D)
This is an algebraic fit, due to Pratt, based on the journal article
V. Pratt, "Direct least-squares fitting of algebraic surfaces",
Computer Graphics, Vol. 21, pages 145-152 (1987)
Input: data - the class of data (contains the given points):
data.n - the number of data points
data.X[] - the array of X-coordinates
data.Y[] - the array of Y-coordinates
Output:
circle - parameters of the fitting circle:
circle.a - the X-coordinate of the center of the fitting circle
circle.b - the Y-coordinate of the center of the fitting circle
circle.r - the radius of the fitting circle
circle.s - the root mean square error (the estimate of sigma)
circle.j - the total number of iterations
The method is based on the minimization of the function
F = sum [(x-a)^2 + (y-b)^2 - R^2]^2 / R^2
This method is more balanced than the simple Kasa fit.
It works well whether data points are sampled along an entire circle or
along a small arc.
It still has a small bias and its statistical accuracy is slightly
lower than that of the geometric fit (minimizing geometric distances).
It provides a good initial guess for a subsequent geometric fit.
Nikolai Chernov (September 2012)
*/
{
int i,iter,IterMAX=99;
reals Xi,Yi,Zi;
reals Mz,Mxy,Mxx,Myy,Mxz,Myz,Mzz,Cov_xy,Var_z;
reals A0,A1,A2,A22;
reals Dy,xnew,x,ynew,y;
reals DET,Xcenter,Ycenter;
Circle circle;
data.means(); // Compute x- and y- sample means (via a function in the class "data")
// computing moments
Mxx=Myy=Mxy=Mxz=Myz=Mzz=0.;
for (i=0; i<data.n; i++)
{
Xi = data.X[i] - data.meanX; // centered x-coordinates
Yi = data.Y[i] - data.meanY; // centered y-coordinates
Zi = Xi*Xi + Yi*Yi;
Mxy += Xi*Yi;
Mxx += Xi*Xi;
Myy += Yi*Yi;
Mxz += Xi*Zi;
Myz += Yi*Zi;
Mzz += Zi*Zi;
}
Mxx /= data.n;
Myy /= data.n;
Mxy /= data.n;
Mxz /= data.n;
Myz /= data.n;
Mzz /= data.n;
// computing coefficients of the characteristic polynomial
Mz = Mxx + Myy;
Cov_xy = Mxx*Myy - Mxy*Mxy;
Var_z = Mzz - Mz*Mz;
A2 = Four*Cov_xy - Three*Mz*Mz - Mzz;
A1 = Var_z*Mz + Four*Cov_xy*Mz - Mxz*Mxz - Myz*Myz;
A0 = Mxz*(Mxz*Myy - Myz*Mxy) + Myz*(Myz*Mxx - Mxz*Mxy) - Var_z*Cov_xy;
A22 = A2 + A2;
// finding the root of the characteristic polynomial
// using Newton's method starting at x=0
// (it is guaranteed to converge to the right root)
for (x=0.,y=A0,iter=0; iter<IterMAX; iter++) // usually, 4-6 iterations are enough
{
Dy = A1 + x*(A22 + 16.*x*x);
xnew = x - y/Dy;
if ((xnew == x)||(!isfinite(xnew))) break;
ynew = A0 + xnew*(A1 + xnew*(A2 + Four*xnew*xnew));
if (abs(ynew)>=abs(y)) break;
x = xnew; y = ynew;
}
// computing paramters of the fitting circle
DET = x*x - x*Mz + Cov_xy;
Xcenter = (Mxz*(Myy - x) - Myz*Mxy)/DET/Two;
Ycenter = (Myz*(Mxx - x) - Mxz*Mxy)/DET/Two;
// assembling the output
circle.a = Xcenter + data.meanX;
circle.b = Ycenter + data.meanY;
circle.r = sqrt(Xcenter*Xcenter + Ycenter*Ycenter + Mz + x + x);
circle.s = Sigma(data,circle);
circle.i = 0;
circle.j = iter; // return the number of iterations, too
return circle;
}Taubin fit
Circle CircleFitByTaubin (Data& data)
/*
Circle fit to a given set of data points (in 2D)
This is an algebraic fit, due to Taubin, based on the journal article
G. Taubin, "Estimation Of Planar Curves, Surfaces And Nonplanar
Space Curves Defined By Implicit Equations, With
Applications To Edge And Range Image Segmentation",
IEEE Trans. PAMI, Vol. 13, pages 1115-1138, (1991)
Input: data - the class of data (contains the given points):
data.n - the number of data points
data.X[] - the array of X-coordinates
data.Y[] - the array of Y-coordinates
Output:
circle - parameters of the fitting circle:
circle.a - the X-coordinate of the center of the fitting circle
circle.b - the Y-coordinate of the center of the fitting circle
circle.r - the radius of the fitting circle
circle.s - the root mean square error (the estimate of sigma)
circle.j - the total number of iterations
The method is based on the minimization of the function
sum [(x-a)^2 + (y-b)^2 - R^2]^2
F = -------------------------------
sum [(x-a)^2 + (y-b)^2]
This method is more balanced than the simple Kasa fit.
It works well whether data points are sampled along an entire circle or
along a small arc.
It still has a small bias and its statistical accuracy is slightly
lower than that of the geometric fit (minimizing geometric distances),
but slightly higher than that of the very similar Pratt fit.
Besides, the Taubin fit is slightly simpler than the Pratt fit
It provides a very good initial guess for a subsequent geometric fit.
Nikolai Chernov (September 2012)
*/
{
int i,iter,IterMAX=99;
reals Xi,Yi,Zi;
reals Mz,Mxy,Mxx,Myy,Mxz,Myz,Mzz,Cov_xy,Var_z;
reals A0,A1,A2,A22,A3,A33;
reals Dy,xnew,x,ynew,y;
reals DET,Xcenter,Ycenter;
Circle circle;
data.means(); // Compute x- and y- sample means (via a function in the class "data")
// computing moments
Mxx=Myy=Mxy=Mxz=Myz=Mzz=0.;
for (i=0; i<data.n; i++)
{
Xi = data.X[i] - data.meanX; // centered x-coordinates
Yi = data.Y[i] - data.meanY; // centered y-coordinates
Zi = Xi*Xi + Yi*Yi;
Mxy += Xi*Yi;
Mxx += Xi*Xi;
Myy += Yi*Yi;
Mxz += Xi*Zi;
Myz += Yi*Zi;
Mzz += Zi*Zi;
}
Mxx /= data.n;
Myy /= data.n;
Mxy /= data.n;
Mxz /= data.n;
Myz /= data.n;
Mzz /= data.n;
// computing coefficients of the characteristic polynomial
Mz = Mxx + Myy;
Cov_xy = Mxx*Myy - Mxy*Mxy;
Var_z = Mzz - Mz*Mz;
A3 = Four*Mz;
A2 = -Three*Mz*Mz - Mzz;
A1 = Var_z*Mz + Four*Cov_xy*Mz - Mxz*Mxz - Myz*Myz;
A0 = Mxz*(Mxz*Myy - Myz*Mxy) + Myz*(Myz*Mxx - Mxz*Mxy) - Var_z*Cov_xy;
A22 = A2 + A2;
A33 = A3 + A3 + A3;
// finding the root of the characteristic polynomial
// using Newton's method starting at x=0
// (it is guaranteed to converge to the right root)
for (x=0.,y=A0,iter=0; iter<IterMAX; iter++) // usually, 4-6 iterations are enough
{
Dy = A1 + x*(A22 + A33*x);
xnew = x - y/Dy;
if ((xnew == x)||(!isfinite(xnew))) break;
ynew = A0 + xnew*(A1 + xnew*(A2 + xnew*A3));
if (abs(ynew)>=abs(y)) break;
x = xnew; y = ynew;
}
// computing paramters of the fitting circle
DET = x*x - x*Mz + Cov_xy;
Xcenter = (Mxz*(Myy - x) - Myz*Mxy)/DET/Two;
Ycenter = (Myz*(Mxx - x) - Mxz*Mxy)/DET/Two;
// assembling the output
circle.a = Xcenter + data.meanX;
circle.b = Ycenter + data.meanY;
circle.r = sqrt(Xcenter*Xcenter + Ycenter*Ycenter + Mz);
circle.s = Sigma(data,circle);
circle.i = 0;
circle.j = iter; // return the number of iterations, too
return circle;
}Hyper fit
Circle CircleFitByHyper (Data& data)
/*
Circle fit to a given set of data points (in 2D)
This is an algebraic fit based on the journal article
A. Al-Sharadqah and N. Chernov, "Error analysis for circle fitting algorithms",
Electronic Journal of Statistics, Vol. 3, pages 886-911, (2009)
It is an algebraic circle fit with "hyperaccuracy" (with zero essential bias).
The term "hyperaccuracy" first appeared in papers by Kenichi Kanatani around 2006
Input: data - the class of data (contains the given points):
data.n - the number of data points
data.X[] - the array of X-coordinates
data.Y[] - the array of Y-coordinates
Output:
circle - parameters of the fitting circle:
circle.a - the X-coordinate of the center of the fitting circle
circle.b - the Y-coordinate of the center of the fitting circle
circle.r - the radius of the fitting circle
circle.s - the root mean square error (the estimate of sigma)
circle.j - the total number of iterations
This method combines the Pratt and Taubin fits to eliminate the essential bias.
It works well whether data points are sampled along an entire circle or
along a small arc.
Its statistical accuracy is theoretically higher than that of the Pratt fit
and Taubin fit, but practically they all return almost identical circles
(unlike the Kasa fit that may be grossly inaccurate).
It provides a very good initial guess for a subsequent geometric fit.
Nikolai Chernov (September 2012)
*/
{
int i,iter,IterMAX=99;
reals Xi,Yi,Zi;
reals Mz,Mxy,Mxx,Myy,Mxz,Myz,Mzz,Cov_xy,Var_z;
reals A0,A1,A2,A22;
reals Dy,xnew,x,ynew,y;
reals DET,Xcenter,Ycenter;
Circle circle;
data.means(); // Compute x- and y- sample means (via a function in the class "data")
// computing moments
Mxx=Myy=Mxy=Mxz=Myz=Mzz=0.;
for (i=0; i<data.n; i++)
{
Xi = data.X[i] - data.meanX; // centered x-coordinates
Yi = data.Y[i] - data.meanY; // centered y-coordinates
Zi = Xi*Xi + Yi*Yi;
Mxy += Xi*Yi;
Mxx += Xi*Xi;
Myy += Yi*Yi;
Mxz += Xi*Zi;
Myz += Yi*Zi;
Mzz += Zi*Zi;
}
Mxx /= data.n;
Myy /= data.n;
Mxy /= data.n;
Mxz /= data.n;
Myz /= data.n;
Mzz /= data.n;
// computing the coefficients of the characteristic polynomial
Mz = Mxx + Myy;
Cov_xy = Mxx*Myy - Mxy*Mxy;
Var_z = Mzz - Mz*Mz;
A2 = Four*Cov_xy - Three*Mz*Mz - Mzz;
A1 = Var_z*Mz + Four*Cov_xy*Mz - Mxz*Mxz - Myz*Myz;
A0 = Mxz*(Mxz*Myy - Myz*Mxy) + Myz*(Myz*Mxx - Mxz*Mxy) - Var_z*Cov_xy;
A22 = A2 + A2;
// finding the root of the characteristic polynomial
// using Newton's method starting at x=0
// (it is guaranteed to converge to the right root)
for (x=0.,y=A0,iter=0; iter<IterMAX; iter++) // usually, 4-6 iterations are enough
{
Dy = A1 + x*(A22 + 16.*x*x);
xnew = x - y/Dy;
if ((xnew == x)||(!isfinite(xnew))) break;
ynew = A0 + xnew*(A1 + xnew*(A2 + Four*xnew*xnew));
if (abs(ynew)>=abs(y)) break;
x = xnew; y = ynew;
}
// computing paramters of the fitting circle
DET = x*x - x*Mz + Cov_xy;
Xcenter = (Mxz*(Myy - x) - Myz*Mxy)/DET/Two;
Ycenter = (Myz*(Mxx - x) - Mxz*Mxy)/DET/Two;
// assembling the output
circle.a = Xcenter + data.meanX;
circle.b = Ycenter + data.meanY;
circle.r = sqrt(Xcenter*Xcenter + Ycenter*Ycenter + Mz - x - x);
circle.s = Sigma(data,circle);
circle.i = 0;
circle.j = iter; // return the number of iterations, too
return circle;
}Data class (for data points)
//
// data.h
//
/************************************************************************
DECLARATION OF THE CLASS DATA
************************************************************************/
// Class for Data
// A data has 5 fields:
// n (of type int), the number of data points
// X and Y (arrays of type reals), arrays of x- and y-coordinates
// meanX and meanY (of type reals), coordinates of the centroid (x and y sample means)
class Data
{
public:
int n;
reals *X; //space is allocated in the constructors
reals *Y; //space is allocated in the constructors
reals meanX, meanY;
// constructors
Data();
Data(int N);
Data(int N, reals X[], reals Y[]);
// routines
void means(void);
void center(void);
void scale(void);
void print(void);
// destructors
~Data();
};
/************************************************************************
BODY OF THE MEMBER ROUTINES
************************************************************************/
// Default constructor
Data::Data()
{
n=0;
X = new reals[n];
Y = new reals[n];
for (int i=0; i<n; i++)
{
X[i]=0.;
Y[i]=0.;
}
}
// Constructor with assignment of the field N
Data::Data(int N)
{
n=N;
X = new reals[n];
Y = new reals[n];
for (int i=0; i<n; i++)
{
X[i]=0.;
Y[i]=0.;
}
}
// Constructor with assignment of each field
Data::Data(int N, reals dataX[], reals dataY[])
{
n=N;
X = new reals[n];
Y = new reals[n];
for (int i=0; i<n; i++)
{
X[i]=dataX[i];
Y[i]=dataY[i];
}
}
// Routine that computes the x- and y- sample means (the coordinates of the centeroid)
void Data::means(void)
{
meanX=0.; meanY=0.;
for (int i=0; i<n; i++)
{
meanX += X[i];
meanY += Y[i];
}
meanX /= n;
meanY /= n;
}
// Routine that centers the data set (shifts the coordinates to the centeroid)
void Data::center(void)
{
reals sX=0.,sY=0.;
int i;
for (i=0; i<n; i++)
{
sX += X[i];
sY += Y[i];
}
sX /= n;
sY /= n;
for (i=0; i<n; i++)
{
X[i] -= sX;
Y[i] -= sY;
}
meanX = 0.;
meanY = 0.;
}
// Routine that scales the coordinates (makes them of order one)
void Data::scale(void)
{
reals sXX=0.,sYY=0.,scaling;
int i;
for (i=0; i<n; i++)
{
sXX += X[i]*X[i];
sYY += Y[i]*Y[i];
}
scaling = sqrt((sXX+sYY)/n/Two);
for (i=0; i<n; i++)
{
X[i] /= scaling;
Y[i] /= scaling;
}
}
// Printing routine
void Data::print(void)
{
cout << endl << "The data set has " << n << " points with coordinates :"<< endl;
for (int i=0; i<n-1; i++) cout << setprecision(7) << "(" << X[i] << ","<< Y[i] << "), ";
cout << "(" << X[n-1] << ","<< Y[n-1] << ")\n";
}
// Destructor
Data::~Data()
{
delete[] X;
delete[] Y;
}Circle class (for circle parameters)
查看代码
//
// circle.h
//
/************************************************************************
DECLARATION OF THE CLASS CIRCLE
************************************************************************/
// Class for Circle
// A circle has 7 fields:
// a, b, r (of type reals), the circle parameters
// s (of type reals), the estimate of sigma (standard deviation)
// g (of type reals), the norm of the gradient of the objective function
// i and j (of type int), the iteration counters (outer and inner, respectively)
class Circle
{
public:
// The fields of a Circle
reals a, b, r, s, g, Gx, Gy;
int i, j;
// constructors
Circle();
Circle(reals aa, reals bb, reals rr);
// routines
void print(void);
// no destructor we didn't allocate memory by hand.
};
/************************************************************************
BODY OF THE MEMBER ROUTINES
************************************************************************/
// Default constructor
Circle::Circle()
{
a=0.; b=0.; r=1.; s=0.; i=0; j=0;
}
// Constructor with assignment of the circle parameters only
Circle::Circle(reals aa, reals bb, reals rr)
{
a=aa; b=bb; r=rr;
}
// Printing routine
void Circle::print(void)
{
cout << endl;
cout << setprecision(10) << "center (" <<a <<","<< b <<") radius "
<< r << " sigma " << s << " gradient " << g << " iter "<< i << " inner " << j << endl;
}查看代码
#include <iostream>
#include <cmath>
#include <limits>
#include <iomanip>
#include <cstdlib>
using namespace std;
// define precision by commenting out one of the two lines:
typedef double reals; // defines reals as double (standard for scientific calculations)
//typedef long double reals; // defines reals as long double
// Note: long double is an 80-bit format (more accurate, but more memory demanding and slower)
typedef long long integers;
// next define some frequently used constants:
const reals One=1.0,Two=2.0,Three=3.0,Four=4.0,Five=5.0,Six=6.0,Ten=10.0;
//const reals One=1.0L,Two=2.0L,Three=3.0L,Four=4.0L,Five=5.0L,Six=6.0L,Ten=10.0L;
const reals Pi=3.141592653589793238462643383L;
const reals REAL_MAX=numeric_limits<reals>::max();
const reals REAL_MIN=numeric_limits<reals>::min();
const reals REAL_EPSILON=numeric_limits<reals>::epsilon();
// next define some frequently used functions:
template<typename T>
inline T SQR(T t) { return t*t; };
reals pythag(reals a, reals b)
{
reals absa=abs(a), absb=abs(b);
if (absa > absb) return absa*sqrt(One+SQR(absb/absa));
else return (absb == 0.0 ? 0.0 : absb*sqrt(One+SQR(absa/absb)));
}
//#include "RandomNormalPair.cpp" // routine for generating normal random numbers查看代码
void RandomNormalPair( reals& x, reals& y )
/*
Generator of pseudo-random numbers
with standard normal distribution
based on Box-Muller transformation
"reals" can be replaced by "float",
"double", or "long double"; or it
can be predefined as one of these types
Input: none
Output: two real values, x and y,
that are random, independent, and
have standard normal distribution
(with mean 0 and variance 1)
Call:
RandomNormalPair(x,y);
Uses standard C++ random generator rand()
To reseed the generator rand(), call
srand ( (unsigned)time(NULL) );
before you start calling this function
Nikolai Chernov, November 2011
*/
{
reals rand1,rand2,wrand;
/*
// version 1, by direct calculation (slower)
reals pi=3.141592653589793;
rand1 = (reals)rand()/RAND_MAX;
rand2 = (reals)rand()/RAND_MAX;
x = sqrt(-Two*log(rand1))*cos(Two*pi*rand2);
y = sqrt(-Two*log(rand1))*sin(Two*pi*rand2);
*/
// version 2, in polar form
// (faster and more stable numerically)
do {
rand1 = Two*rand()/RAND_MAX - One;
rand2 = Two*rand()/RAND_MAX - One;
wrand = rand1*rand1 + rand2*rand2;
} while (wrand >= One);
wrand = sqrt( (-Two*log(wrand) ) / wrand );
x = rand1 * wrand;
y = rand2 * wrand;
}
//*********************** SimulateArc ******************************
void SimulateArc(Data& data, reals a, reals b, reals R, reals theta1, reals theta2, reals sigma)
/*
Simulate data points equally spaced along a circular arc with Gaussian noise
input:
a,b the coordinates of the center of the circle
R the radius of circle
theta1 first endpoint of the arc (in radians)
theta2 second endpoint of the arc (in radians)
sigma noise level (standard deviation of residuals)
*/
{
int N=data.n; reals theta,dx,dy;
for (int i=0; i<N; i++)
{
theta = theta1 + (theta2 - theta1)*i/(N-1);
// isotropic Gaussian noise
RandomNormalPair(dx,dy);
data.X[i] = a + R*cos(theta) + sigma*dx;
data.Y[i] = b + R*sin(theta) + sigma*dy;
}
}
//********************* SimulateRandom ****************************
void SimulateRandom(Data& data, reals Window)
/*
Simulate data points with uniform distribution
in the square |x|<Window, |y|<Window
input:
nPoints the number of data points
*/
{
//Data data(nPoints);
for (int i=0; i<data.n; i++)
{
data.X[i] = Window*(Two*rand()/RAND_MAX - One);
data.Y[i] = Window*(Two*rand()/RAND_MAX - One);
}
}
//****************** Sigma ************************************
//
// estimate of Sigma = square root of RSS divided by N
// gives the root-mean-square error of the geometric circle fit
reals Sigma (Data& data, Circle& circle)
{
reals sum=0.,dx,dy;
for (int i=0; i<data.n; i++)
{
dx = data.X[i] - circle.a;
dy = data.Y[i] - circle.b;
sum += SQR(sqrt(dx*dx+dy*dy) - circle.r);
}
return sqrt(sum/data.n);
}
//****************** SigmaReduced ************************************
//
// estimate of Sigma = square root of RSS divided by N
// gives the root-mean-square error of the geometric circle fit
//
// uses only the center of the circle (a,b), not the radius
// the function computes the optimal radius here
reals SigmaReduced (Data& data, Circle& circle)
{
int i,n=data.n;
reals sum=0.,dx,dy,r,D[n];
for (i=0; i<n; i++)
{
dx = data.X[i] - circle.a;
dy = data.Y[i] - circle.b;
D[i] = sqrt(dx*dx+dy*dy);
sum += D[i];
}
r = sum/n;
for (sum=0., i=0; i<n; i++) sum += SQR(D[i] - r);
return sqrt(sum/n);
}
//****************** SigmaReducedNearLinearCase ****************
//
// estimate of Sigma = square root of RSS divided by N
reals SigmaReducedNearLinearCase (Data& data, Circle& circle)
{
int i,n=data.n;
reals a0,b0,del,s,c,x,y,z,p,t,g,W,Z;
a0 = circle.a-data.meanX; b0 = circle.b-data.meanY;
del = One/sqrt(a0*a0 + b0*b0);
s = b0*del; c = a0*del;
for (W=Z=0.,i=0; i<n; i++)
{
x = data.X[i] - data.meanX;
y = data.Y[i] - data.meanY;
z = x*x + y*y;
p = x*c + y*s;
t = del*z - Two*p;
g = t/(One+sqrt(One+del*t));
W += (z+p*g)/(Two+del*g);
Z += z;
}
W /= n;
Z /= n;
return sqrt(Z-W*(Two+del*del*W));
}
//****************** SigmaReducedForCenteredScaled ****************
//
// estimate of Sigma = square root of RSS divided by N
reals SigmaReducedForCenteredScaled (Data& data, Circle& circle)
{
int i,n=data.n;
reals sum=0.,dx,dy,r;
for (i=0; i<n; i++)
{
dx = data.X[i] - circle.a;
dy = data.Y[i] - circle.b;
sum += sqrt(dx*dx+dy*dy);
}
r = sum/n;
return sqrt(SQR(circle.a)+SQR(circle.b)-r*r+Two);
}
//****************** OptimalRadius ******************************
//
// compute the optimal radius of a circle, given its center (a,b)
reals OptimalRadius (Data& data, Circle& circle)
{
reals Mr=0.,dx,dy;
for (int i=0; i<data.n; i++)
{
dx = data.X[i] - circle.a;
dy = data.Y[i] - circle.b;
Mr += sqrt(dx*dx + dy*dy);
}
return Mr/data.n;
}
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