# OpenCV Ellipse fitting: extract parameters

I have been investigating the `cv::fitEllipse`

function for extracting additional data. I read the article that is cited in the documentation (*Andrew W. Fitzgibbon, R.B.Fisher. A Buyer’s Guide to Conic Fitting. Proc.5th British Machine Vision Conference, Birmingham, pp. 513-522, 1995*which can be found at http://www.bmva.org/bmvc/1995/bmvc-95...).

I explicitly want to extract the `a = [Axx Axy Ayy ...]`

matrix, but the code is so optimized that I cannot identify where these values are. I'm not even sure that the function fom OpenCV 3.0 implements that algorithm. For instance, they only estimate 5 parameters, while the cited paper refers to 6 parameters.

Does anyone has an hint on that?

Alternatively, does anyone have a hint on how I can measure how good my estimated ellipse fits the model? For now, I was relying on the fact that `F(a, x) = 0`

, where `a`

is my ellipse parameter vector, `a = [Axx Axy Ayy ...]`

.