My problem is such that I need to reconstruct a circular surface which is observed from an oblique angle so that it shows in the image as an ellipse. From other image parts I can construct the scale in X and Y directions so that I have knowledge of the expected ratio of the axes of the ellipse. The ellipse in question can be defined by points which cover about 1/3 of its circumference, equally distributed where the shorter axis cuts the circumference.
While in principle it's possible to fit an ellipse using these data points (e.g. using Markwardt's ellipse fitting which implements a flavour of the Levenberg-Marquardt technique), it might return wrong parameters as the ratio of axes is not well defined by the data coverage (the excentricity is around 0.3, the ratio of the axes is about 1.05).
I'm looking for an algorithm which allows to give additional constraints when fitting an ellipse or pointers how to tackle that problem.
Neither a search here nor my google-foo returned anything.
