double[][] cov = estimator.getCovariances(circle);
assertEquals(1.839, cov[0][0], 0.001);
assertEquals(0.731, cov[0][1], 0.001);
assertEquals(cov[0][1], cov[1][0], 1.0e-14);
assertEquals(0.786, cov[1][1], 0.001);
double[] errors = estimator.guessParametersErrors(circle);
assertEquals(1.384, errors[0], 0.001);
assertEquals(0.905, errors[1], 0.001);
// add perfect measurements and check errors are reduced
double cx = circle.getX();